[Exim] PERL_COMMAND parsing problem

the sed expression for getting the PERL_COMMAND in
scripts/Configure-Makefile is evidently not as robust as the one used
elsewhere. It does not work correctly if there is a space at the
beginning of the line (possibly doesn't work other places, also, haven't
checked).

If I have this in Local/Makefile:
PERL_COMMAND=/usr/bin/perl.nosfio
Then Configure-Makefile successfully parses it and tries to run the
command "/usr/bin/perl.nosfio --version".

However, if I have this in Local/Makefile (note leading space):
PERL_COMMAND=/usr/bin/perl.nosfio
Then Configure-Makefile tries to run The command
"PERL_COMMAND=/usr/bin/perl.nosfio --version"

I have many other options in Local/Makefile that have leading spaces and
work correctly. my assumption is that Configure-Makefile is doing special
processing of this variable in order to get the values for PERL_LIBS, etc.

--John