Remove no-op

This expression is not assigned to no variable, and so has no effect.
Pass CC/CFLAGS and CC/CXXFLAGS to configure script separately

Addresses #158.
Merge pull request #159 from lpsinger/cflags-parsing

Pass CC/CFLAGS and CC/CXXFLAGS to configure script separately
Release 1.7.4
Update MANIFEST.in

Added CITATION to tarball Closes #165