MDB Test suite

This provides a primordial version of a test suite for mdb. To run the tests,
run mtest. Tests exist in various subdirectories. The name of the test is
important.

A test must start with either:

 o tst - Indicating that it should exit zero
 o err - Indicating that it should exit non-zero

A test must end with either:

 o mdb - Indicating that the file should be passed as standard input to mdb
 o ksh - Indicating that it should be run with ksh

A test may have an optional .out file which if present indicates that the test
should pass if and only if its standard ouput matches its standar error.