Fixes for MIT pthreads


Docs/manual.texi:
  Update for MIT pthreads and sockets
configure.in:
  Fixed MIT pthreads to use sockets
myisam/mi_check.c:
  Portability fix
myisam/sort.c:
  Portability fix
sql/handler.h:
  Give an error if you use a BLOB(X) where X > 255
sql/mysqld.cc:
  Fixed MIT pthreads to use sockets
sql/sql_table.cc:
  Give an error if you use a BLOB(X) where X > 255
sql/table.cc:
  Fixed problem with BDB tables without keys