[INFO] Buffer/PMC unification - #7 and finito for now

[Leopold Toetsch]

Done.

Buffers and PMCs are Parrot Objects now, sharing a common header, PObj.

The struct members:
- buffer
- buflen
- cache
- version (for GC_DEBUG)
are actually #defines now. This implies that the usage of these names is forbidden in the whole parrot tree.

This rule will last until the final structures are fixed, and somone changes all usage of above data members to the real thing.

Finally I was to lazy to change all ->flags in keys.c and list.c, a macro in these files is used to access flags directly.

make quickfulltest doesn't show any error, nor do perl6 tests.

After the feature freeze/release, we can have a look at DOD/GC & Buffer/PMC memory management functions to look, what can be simplified then.

Please do a "make clean" after checkout.

Have fun,
leo