Fixed compilation on platforms where M_PI is not defined.

In this case we define M_PI ourselves in IECore/Math.h - any files needing the definition of M_PI should therefore include this header.
Replaced "or" with "||" and "and" with "&&".

Although "and" and "or" are actually standard C++, they're not available in MSVC without specific compiler flags. We should stick to using && and || everywhere for consistency anyway.
Python bind fix for MSVC
Removed _MSC_VER #ifdef.

We can use the MSVC compatible code path on Linux/OSX too, which is preferable to maintaining two code paths.
Adding the bind includes to the cpp files so that the symbols do get exported properly
MSVC compile fixes for IECoreGL
Merge pull request #375 from johnhaddon/msvcFixes

MSVC Fixes