Packaging Script: Ensures comtypes has been generated

* If comtypes isn't generated (IE: Wrye Bash never used to display HTML),
  then the generated comtypes files for wx.lib.iewin won't get included by
  py2exe, and those features will not work in the standalone
Packaging Script: git branch details

 * If the current branch doesn't look like a release branch, print a
   warning
 * Prints the current branch name when building
NSIS: w9xpopen handling

 * Only install w9xpopen if a version prior to XP is detected
 * Delete w9xpopen from previous installs if it is not needed