a work-in-progress map modified callback interface (committing because i want to merge the fence stuff)

Added a check that avoids server crash (unhandled exception) when map generation is attempted near limit

--HG--
extra : rebase_source : e8ec407f60711d42d33be4811b2880088f617b5b

mud placed in sunlight no longer instantly turns to grass; also tuned transforming speed a bit (will be made a lot longer when testing is complete)

Moved the temporary mapgen test files and added a modified map.cpp too... These are probably useful in the next mapgen update and shouldn't be lost.

--HG--
rename : src/noise.cpp.new => misc/noise.cpp
rename : src/noise.h.new => misc/noise.h

Add (possibly non-compatible) work-in-progress noise.{h,cpp} so that they won't be accidentally lost. These are useful for upcoming mapgen updates.