Hi,

this patch fixes the names of the icons in the libreoffice desktop 
files, installs additional desktop files for “math” and the 
“startcenter”, and tunes the build configuration (enable liblangtag, 
enable parallel build -- seems to work fine on my machine).

It's a bit of everything, not sure if it should be split into 2 
commits (one for the desktop files & icons, one for the build 
options)?

cheers,

Thomas