add LINUX_OSRELEASE to bsd.linux-rpm.mk

[John E Hein]

Boris Samorodov wrote at 20:42 +0400 on Apr  1, 2008:
 > Seems that I have change my mind since linux-rpm.mk is too tied to rpm
 > format and dealing with it. The file can't be (easily) used with an
 > average linux port. I tried to convert to using linux-rpm.mk acroread7
 > port. I got a mess. :-(
 > 
 > Well, what about new bsd.linux-apps.rpm?

Ermm... typo?  Change that to 'bsd.linux-apps.mk' and it sounds
good to me ;)

I've always disliked specifying the package file format in the linux
.mk file name.