I added an implementation of C-functions "sgemm_" and "dgemm_" that call Numpy C-API functions to perform matrix product when BLAS is explicitely disabled (with theano flag "blas.ldflags" set to empty).

This can be tested with:
THEANO_FLAGS=blas.ldflags= nosetests theano/tensor/nnet/tests/test_abstract_conv.py:TestCorrConv2d