Linux binary installer does not check for required C libs (apparently)

[dcoutts]

Had a user on IRC who had installed the latest platform on their ubuntu system, and then got a linker error complaining about -lz because they did not have the system package for the zlib C lib installed. The installer script ought to check this (like Cabal would check when configuring to build from source).

One possibility here is that we could use the ghc-pkg database to get the list of all the extra-libraries needed by all the packages we're installing/registering, and then check all of those in one go.

[mzero]

The activate-hs script would be the right place to put this.
Anyone ( @dcoutts ) want to code up a pull request?

[gbaz]

@dagit more :-)