Runtime string support clean up and refactoring.

This commit moves the launcher-shared C string functions into
chpl-string-support.[ch] and changes the Makefile and other files
appropriately.  I took the opportunity to pare down the #included
files in chpl-string.c and chpl-string-support.c to only what is
needed.

In addition, some remaining invalid uses of chpl_string are removed.
Merge branch 'master' of github.com:chapel-lang/chapel into test
Further re-shuffling.
Add comments at the top of chpl-string-support.[ch] about the file and
possibly renaming of the file as well as the functions within.
Merge branch 'master' of github.com:chapel-lang/chapel into test
Merge pull request #118 from sungeunchoi/test

Runtime string support clean up and refactoring

[reviewed by David]

This commit moves the launcher-shared C string functions into chpl-string-support.[ch] and changes the Makefile and other files appropriately. I took the opportunity to pare down the #included files in chpl-string.c and chpl-string-support.c to only what is needed. In addition, some remaining invalid uses of chpl_string are removed.

We should consider renaming chpl-string-support.[ch] and the functions within at some point when the string stuff has settled down.