Catchall routine to clean up problem MM[SK]/Make macros. Expands macros
in any directory specification, in order to avoid juxtaposing two
VMS-syntax directories when MM[SK] is run. Also expands expressions which
are all macro, so that we can tell how long the expansion is, and avoid
overrunning DCL's command buffer when MM[KS] is running.
If optional second argument has a TRUE value, then the return string is
a VMS-syntax directory specification, if it is FALSE, the return string
is a VMS-syntax file specification, and if it is not specified, fixpath()
checks to see whether it matches the name of a directory in the current
default directory, and returns a directory or file specification accordingly.
Concatenates a list of file specifications, and returns the result as a
VMS-syntax directory specification. No check is made for ``impossible''
cases (e.g. elements other than the first being absolute filespecs).