Source code files included in installed distribution

[malthe]

Steps to reproduce:

1. Install using "pip" from source distribution.

Expected behaviour: [What was expected to happen.]

Only Python module files and binary code is installed in site-packages.

Actual behaviour: [What actually happened.]

Source code (e.g. "session.c") is included.

Additional info: [Include version of libssh2 and any other relevant information.]

[pkittenis]

Source distribution will include source files.