Support features: qt5, git, debug flag

* qt5: The support should work on #uim-vi-1.9 branch
* debug: Turn on debug stuff. Basic support
* git: Build with git source. See example for details

And example:
  WITHOUT_THESLINUX_SOURCES=1 \
  PACKAGE_TAG=uim-vi-1.9 \
  PACKAGE_FEATURE=qt5-debug-git-cfd6013ebc \
  s-makepg

Please note "PACKAGE_TAG=uim-vi-1.9". The release number
is always 1, unless you specify it manually (1.9-123).