Fixes problem with pi (and i,j,k) not being retained as a named constant, but being replaced by their values.  This was introduced accidentally by commit 261ba03f0e87c867efdbf32b8e2692e1485cdd1.
Merge pull request #25 from dpvc/fix-pi

Fixes problem with pi (and i,j,k) not being retained as a named constant
update version to 2.7