MageKing17's patch for callsigns not resetting when the mission is cleared (Mantis #2934)

git-svn-id: svn://svn.icculus.org/fs2open@10863 387891d4-d844-0410-90c0-e4c51a9137d3
from MageKing17: choose alt_names and callsigns by array index instead of substring; fixes Mantis #2934

git-svn-id: svn://svn.icculus.org/fs2open@10864 387891d4-d844-0410-90c0-e4c51a9137d3
Yarn's fix for Mantis #2362 (scale images properly with show-subtitle-image)

git-svn-id: svn://svn.icculus.org/fs2open@10865 387891d4-d844-0410-90c0-e4c51a9137d3
Remove a tautological Assert(), which cannot be triggered due to the type

git-svn-id: svn://svn.icculus.org/fs2open@10866 387891d4-d844-0410-90c0-e4c51a9137d3
Fix Clang warnings about incorrect type given different pointer sizes for the architecture. Use the standard compliant ptrdiff_t

git-svn-id: svn://svn.icculus.org/fs2open@10867 387891d4-d844-0410-90c0-e4c51a9137d3
Fix Mantis #3070, courtesy of Yarn.

git-svn-id: svn://svn.icculus.org/fs2open@10868 387891d4-d844-0410-90c0-e4c51a9137d3