Fix small leak in pythonui.c python_ui_setup_callback()

Another use of the recent routine gutils/fsys.c :: getFontForgeUserDir()
that requires a free() of the newly allocated string after use.

Note that there was an unprotected path if a NULL was returned from
getFontForgeUserDir().  The old code would have tried to use the null
pointer.  The fix protects against that, but rather does 'nothing' if
NULL is returned.  Maybe it should blow up horrible bad instead?
Fix a crash that occurs when one selects no glyph from the picker when kerning by classes.
Merge pull request #1627 from fontforge/metrics_crash_1

Fix a class kerning crash.
Use xmlNewTextChild when feeding unescaped text to libxml.
Update CONTRIBUTING.md
Small leak and ineffective code GIOGetMimeType()

Interesting result from valgrind revealed that
 - a line of code *was* being executed,
 - but that that line's work was being ignored

Fix changes the line to be an assignment, and then adds the required
intermediate g_free().

This typo didn't alter the final result, as the third (!) call to
routine g_content_type_guess() gave the correct final result.  (I checked)

Still, @khaledhosny might want to check the original code to see if
this typo exists there also.
Handle non-integer private PostScript values a little more liberally.
Avoid crashing on invalid lib data.
Null-terminate private value strings correctly.
Merge pull request #1630 from tshinnic/leak_giogetmimetype_wow

Small leak and ineffective code GIOGetMimeType()
issue878 later comment leading with Stop pesky phantom windows from appearing.

The nodejs and python processes are automatically cleaned up when you
close fontforge. A crash during character manipulation was also fixed.

The "open" and "node" paths on OSX are to be tested once I get an osx
build going again.
cleanup
Merge pull request #1636 from monkeyiq/2014/aug/878v1

 issue878 later comment leading with Stop pesky phantom windows from appearing.
collab webfont: try to tell the browser not to cache the ttf files.
Merge pull request #1638 from monkeyiq/2014/aug/1637v2

collab webfont: try to tell the browser not to cache the ttf files.
Merge pull request #1633 from fontforge/issue_1539_part_6

Fix miscellaneous issues handling U. F. O. metadata.
Win32: S_ISLNK doesn't exist (difference in symlink implementation)

Symbolic links on Windows are different to that on POSIX systems. S_ISLNK does
not exist, but should not be needed on Windows anyway.
lookups: selectively process `case` in the metrics window
Use gnulib for strtok_r. See PR #1475 for more info.

This restores Windows XP compatibility.
Merge pull request #1639 from jtanx/win32

Win32: Compilation fixes