Add texMath(Type) to avoid recursion error

[d-torrance]

This fixes a recursion error which I think may have been introduced in #3845 (when texMath(Ring) was split off from texMath(HashTable)):

i1 : texMath HashTable
stdio:2:7:(3): error: recursion limit of 300 exceeded

The issue is that types are mutable hash tables, and the texMath method for mutable hash tables calls texMath on the class, which is itself a mutable hash table, causing the infinite recursion.

[pzinn]

ah yes this is a strange bug. on my branch I have

texMath HashTable := H -> if H.?texMath then H.texMath else (
    if hasAttribute(H, ReverseDictionary) then texMath toString getAttribute(H, ReverseDictionary)
    else if isMutable H then texMathMutable H
    else texMath class H | texMath apply(sortByName pairs H, (k, v) -> k => v))

note the extra 2nd line.
not sure why this didn't make it in #3845.
I think this is a better fix...

[pzinn]

more precisely, here's the diff:

199,209c223,226
< texMath HashTable := H -> (
<     if isMutable H then texMathMutable H
<     else texMath class H | texMath apply(sortByName pairs H, (k, v) -> k => v)
<     )
< 
< texMath RingFamily :=
< texMath Ring := R -> (
<     if R.?texMath then R.texMath
<     else if hasAttribute(R, ReverseDictionary) then texMath toString getAttribute(R, ReverseDictionary)
<     else (lookup(texMath,HashTable)) R -- should never happen
<     )
---
> texMath HashTable := H -> if H.?texMath then H.texMath else (
>     if hasAttribute(H, ReverseDictionary) then texMath toString getAttribute(H, ReverseDictionary)
>     else if isMutable H then texMathMutable H
>     else texMath class H | texMath apply(sortByName pairs H, (k, v) -> k => v))

not sure why I decided to split Ring/RingFamily from HashTable... I think it's better to reunite them.

[d-torrance]

I've pushed a new proposal, removing texMath(Ring) and replacing it with texMath(MutableHashTable). This also lets us simplify texMath(HashTable) since we can remove the isMutable check.