Mscgen extension incompatibility with Sphinx 1.3

[flg]

I ran into an issue with mscgen extension when upgrading from Sphinx 1.2.3 to Sphinx 1.3b3.

The test to determine if the invoking builder is latex or else is (render_msc function, line 117 of mscgen.py):
if hasattr(self.builder, 'imgpath'):
But it should be:
if self.builder.format != 'latex':

I guess the Latex builder in 1.3b3 as the imgpath attribute, that it did not have in 1.2.3.