marco 1.22.2 release

Changes since the last release: v1.22.1...v1.22.2

marco 1.22.2

tx: sync with transifex
bump LT_VERSION_INFO
libmarco-private: add version information
add support for invisible borders
frames: avoid deprecated 'gtk_widget_set_double_buffered'
window: avoid clang warning: garbage value
ui: always set the frame background to None
libmetacity: use cairo to render gradient
gradient: sync code with mutter before it was removed