Update WinSparkle in Windows build.
Update the changelogs.
New option for disabling WinSparkle in Windows build.
Fixes toward a 64-bit Windows build.

* Allow disabling the 32-bit Perl, SILC, Sametime and crash report libraries.
* Select bitness for Bonjour, WinSparkle and LibSSP.
* Handle a 64-bit Pidgin++ in the NSIS installer.
More work for the 64-bit Windows build.

* Replace --x64-build with automatic GCC bitness detection.
* Use bitness for the default staging and output directories.
* Add bitness to the names of the output files.
* Indicate bitness in the NSIS installer.
* Other minor changes.
Implement a 64-bit version and update the Windows GTK+ bundle.

GTK+ has been updated from 2.24.24 to 2.24.25. Some of its dependencies were also updated. The 64-bit bundle currently cannot work because the GTK+ libraries against which Pidgin++ gets linked is 32-bit. Pidgin Windev needs to download a 64-bit version of the GTK+ 2.24 development bundle, however this does not seem to be available.
Small fix for GTK+ installation in the Windows offline installer.
Fix integration of the 64-bit LibSSP in Windows build.

Either libgcc_s_dw2 or libgcc_s_seh is now used, depending on the bitness.
Show application bitness in about dialog under Windows.
Small change for the default target directory in Windows build.
Better integration with MSYS2.

* The MSYS2 versions of GTK+ and many other dependencies are now used.
* The new option --pkgbuild now allows creating a pacman package.
Upstream version 2.10.10.
Update the translation template.
Small whitespace cleanup.
Update the changelogs.
Merge upstream version 2.10.10.

The po files were not merged, just the translation template. Translations will be handled by Launchpad.