More generally, clean-up the various batch files we have.
scripts/mdb.bat.in:
Ensure that the value of MERCURY_DEBUGGER_INIT environment variable does
*not* include double quotes, otherwise the path to the mdbrc file will
be incorrect.
scripts/*.bat.in:
Require command extensions to be enabled. This is the default on
all Windows systems we support; explicitly enabling them is just in case
the user turns them off for some reason.
Don't disable echoing twice.
Quote the entire argument to the set command; this should avoid double
quotes ending up where we don't want them.
Update copyright notices.
f7921d7b47
