xmlto: add TEST with "make check", add cmd:cmp to BUILD_PREREQUIRES.
xmlto: add TEST with "make check", add cmd:cmp to BUILD_PREREQUIRES.

cmd:cmp is required for running "make check".
While at it, also sorted BUILD_PREREQUIRES alphabetically.

Begasus/haikuports,haikuports/haikuports,nielx/haikuports,haikuports/haikuports,moochris/haikuports,koletzky/haikuports,Begasus/haikuports,Begasus/haikuports,moochris/haikuports,nielx/haikuports,miqlas/haikuports,miqlas/haikuports,moochris/haikuports,Begasus/haikuports,haikuports/haikuports,koletzky/haikuports,Begasus/haikuports,haikuports/haikuports,nielx/haikuports,miqlas/haikuports,haikuports/haikuports,koletzky/haikuports