src\thirdparty\LAVFilters\build_lavfilters.bat: Keep the style consistent.
installer: reindent and remove commented code.
Batch files: Don't initialize empty variable.

This commit fixes build scripts on Windows XP.
Update VirtualDub to v1.10.4-test11.
Initialize variables.
Run astyle.
Shave off a few more bytes from png files.
Add Windows 8.1 ID in the manifest files.