Replace plugincommon.h with that of MapAndreas

I don't know where the old file came from but this one was copied from
MapAndreas v1.0 beta source code.

The only difference between the two is that this one checks for LINUX
instead of __LINUX__, and indeed it should be LINUX, even the error
message says so.
Merge pull request #1 from Zeex/original

Replace plugincommon.h with that of MapAndreas
Found the original files in MapAndreas.
Merge pull request #2 from udan11/original

Original