clean up cabs single code
Fixing a bug where mpqc build only uses 1 process to build libint.
Merge branch 'taexp' of https://github.com/ValeevGroup/mpqc into taexp
Merge pull request #22 from pchong90/master

cabs single implementation using TA expression
Instead of using the sometimes-broken intra-Ref locking use an explicit lock. Closes #24
Merge branch 'taexp' of https://github.com/ValeevGroup/mpqc into taexp
Merge branch 'taexp' of https://github.com/ValeevGroup/mpqc into dev
fix the lock issue when evaluating integral