Revert "build: use %PYTHON% instead of python"
Revert "build: use %PYTHON% instead of python"

This reverts commit 91943a99d534e67f6b7a7a3be45206afdb3fbf75.

Old commit cherry-picked in but found to cause problems with .msi
creation on Windows.
Original change is mostly pointless because V8 hard-wires
`python` anyway.

PR-URL: https://github.com/iojs/io.js/pull/1475
Reviewed-By: Ben Noordhuis <59bd0a3ff43b32849b319e645d4798d8a5d1e889@bnoordhuis.nl>

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node