[mythtv] FIX: building svn version of myth on gentoo and using latest version of emerge

[Simon Kenyon]

you might have noticed that it checks out the entire source each time it is 
built! this will increase the load on cvs.mythtv.org and is completely 
unnecessary.

my solution is to change myth-svn.eclass to set the value below:

ESVN_STORE_DIR="${BUILD_PREFIX}/svn-src"

this puts the svn source in /var/tmp/portage/svn-src instead of in the build 
tree (which gets deleted after the build)

hope this helps

regards
-- 
simon