Merge branch 'master' into release-4.2

* master:
  Cherry pick fc54014
  Bump Copyright year.
  Change package loading order to account for TeXLive 2016
  Cherry pick 54bc8b8
  Load PlainTeX version of xstring
  Cherry pick ca8b226
  Update Version number
  CHANGELOG entries
  Fix issue with custom spaces
  Reach the translation glyph node by traverse_id()

CHANGELOG.md

@@ -5,7 +5,6 @@ As of v3.0.0 this project adheres to [Semantic Versioning](http://semver.org/).
 [Unreleased][unreleased]
 ### Fixed
 - When the note after an oriscus is at the same pitch, the oriscus will now point downwards by default (see [#1177](https://github.com/gregorio-project/gregorio/issues/1177)).
-- With thanks to Claudio Beccari (@OldClaudio), adding a commentary no longer generates a bad `\hbox` during TeX processing (see [#1202](https://github.com/gregorio-project/gregorio/issues/1202)).
 - When the last note in a score is not in the last syllable, it no longer merges into the (no-note) syllable(s) that follow (see [#1205](https://github.com/gregorio-project/gregorio/issues/1205)).
 
 ### Changed
@@ -97,6 +96,12 @@ As of v3.0.0 this project adheres to [Semantic Versioning](http://semver.org/).
 - `\greemergencystretch`
 
 
+## [4.1.5] - 2016-08-18
+### Fixed
+- Use node.travese_id() to find our desired nodes when doing translation centering across syllables, thereby preventing a conflict with other packages which insert nodes (such as luatex-ja).  See [#1180](https://github.com/gregorio-project/gregorio/issues/1180).
+- Explicitly communicate the rescaling of `\gre@skip@temp@four` back to TeX, thereby fixing the problem with custom spacings.  See [#1199](https://github.com/gregorio-project/gregorio/issues/1199).
+- With thanks to Claudio Beccari (@OldClaudio), adding a commentary no longer generates a bad `\hbox` during TeX processing (see [#1202](https://github.com/gregorio-project/gregorio/issues/1202)).
+
 ## [4.1.4] - 2016-05-29
 ### Fixed
 - Package conflict with luatex-ja also affected the custos.  Have now fixed that problem too.  See [this thread](http://www.mail-archive.com/[email protected]/msg03520.html).

tex/gregoriotex.lua

@@ -392,6 +392,13 @@ local function dump_nodes(head)
   log('--end dump--')
 end
 
+-- helper function for center_translation()
+local function get_first_node_by_id(id, head)
+  for n in traverse_id(id, head) do
+    return n
+  end
+end
+
 local function center_translation(startnode, endnode, ratio, sign, order)
   -- total width between beginning the two centering points
   local total_width = node.dimensions(ratio, sign, order, startnode, endnode)
@@ -406,12 +413,23 @@ local function center_translation(startnode, endnode, ratio, sign, order)
   --    \kern 0pt
   --  }
   --
+  -- While normally we could use startnode.head.next.head.next.head
+  -- to reach the translation (glyph node), packages such as LuaTeX-ja
+  -- may have, for example, prepended a whatsit node to each list
+  -- to store e.g. text direction, moving our translation glyph node to
+  -- startnode.head.next.next.head.next.next.head.next instead.
+  --
+  -- To avoid unpleasant surprises, let's search for each desired node
+  -- by its type:
+  local vlistnode = get_first_node_by_id(vlist, startnode.head)
+  local hlistnode = get_first_node_by_id(hlist, vlistnode.head)
+  local glyphnode = get_first_node_by_id(glyph, hlistnode.head)
   -- hence translation width is:
-  local trans_width = node.dimensions(startnode.head.next.head.next.head)
+  local trans_width = node.dimensions(glyphnode)
   -- now we must transform the kern 0pt into kern Xpt and kern -Xpt where X is:
   local X = (total_width - trans_width) / 2
-  startnode.head.kern = X
-  startnode.head.next.next.kern = -X
+  vlistnode.prev.kern = X
+  vlistnode.next.kern = -X
 end
 
 local debug_types_activated = {['linesglues'] = false}
@@ -1204,6 +1222,7 @@ end
 local function scale_space(factor)
   local skip = tex.getskip('gre@skip@temp@four')
   skip.width = skip.width * factor
+  tex.setskip('gre@skip@temp@four',skip)
   -- should skip.stretch and skip.shink also be scaled?
 end