configure.ag: add back code for msg_control*
configure.ag: add back code for msg_control*

The old macro AM_MONETDB_MSG_CONTROL used to do what's necessary to get
the msg_control* fields in in struct msg.  Since this was dropped in the
removal of MonetDB.m4, the code no longer compiles on Solaris.
(http://monetdb.cwi.nl/testing/projects/monetdb/CurrentNew/logs/39188:13c9a00d05da/GNU-Solaris-sparc/make)
Hopefully this gets Solaris going again.

zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb