package installer: don't display an error message if the user cancelled the operation
adds Windows Imaging Format (.wim, .swm) support
engrampa does not build without packagekit

https://bugzilla.gnome.org/show_bug.cgi?id=634356
7z: changed the compression level options

normal compression : from "-mx=5" to "-mx=7"
maximum compression: from "-mx=7" to "-mx=9 -m0=lzma2"

https://bugzilla.gnome.org/show_bug.cgi?id=635083
Merge pull request #33 from NiceandGently/master

add support for (.wim, .swm), change 7z compression level options + minor improvements