Remove atexit() call on Win32 code path that cause crashes on mapserv

Reported on http://lists.osgeo.org/pipermail/mapserver-dev/2014-October/014269.html
The cleanup done by the atexit() callback is redundant with the one done
by msCleanup(0) at the end of the main().
Fix crash on CONNECTIONTYPE kerneldensity on Windows (#5019)
Fix wrong use of iconv() that caused encoded_text pointer to be moved and corrupted (#5025)
msLayoutTextSymbol(): fix memory corruption in case of failed iconv() (#5025)
Fix for the OGR autostyle unit calculation (#5028)
Merge pull request #5031 from szekerest/issue5028

Fix for the OGR autostyle unit calculation (#5028)
Merge remote-tracking branch 'upstream/master'