Don't include common.gypi from node source tree #1118

node-gyp includes $nodedir/common.gypi when creating build files for an add-on.

Per nodejs/CTC#62 (comment), that probably isn't future-proof and it's a bad idea in general: it makes add-ons pick up compiler and linker settings that aren't intended for them and may be actively harmful. People have filed bug reports about it.

Plan of action:

1. Merge common.gypi into addon.gypi.
2. Strip everything that isn't needed by add-ons.
3. Test the bejebus out of it with citgm.