Fix for #150.

Fix for #150.
We now fallback to Samba-provided CP850 charset module if CP850 or IBM850 does not exist on target system at runtime.
1. Introduce CP850 charset module based on charmaps table from GNU libc 2.2.5
2. Make CP850 charset module shared and build it by default

Should fix Solaris run-time
(This used to be commit e855dc8c9115fa11d315eb34d57722ff612daa11)