[CVS ci] bitwise string vtables; ands, ors opcodes

[Leopold Toetsch]

I have checked in some functionality for string bitwise ops.
- vtable
- B<ands>, B<ors> opcodes
- string_bitwise_{or,and} functions in string.c
- minimal tests
Missing:
- B<xors> ops
- support for perl scalar PMCs
I'd be glad if someone wants to continue that stuff.

Have fun,
leo