Merge branch 'sage_root_repo-5.10.rc0' into master

Conflicts:
	build/deps
	src/bin/sage-env
	src/bin/sage-spkg
5.10.rc0: update git specific files

These currently include
 * VERSION.txt
 * package-version.txt
 * checksums.ini
[FIXUP] can cause issues when testing local changes
[FIXUP] put lapack under src to unify atlas tarball