pass @INC to latexmlc invocation in tests

[dginev]

Ideally this helps with CPANTesters, should be just redundant information for a regular Perl installation.

One key question is whether a call to perl will use the correct version of Perl on CPANTesters. If this fails, there seem to be alternatives that can be tried without a system call, such as:

{
    local @ARGV = qw<param1 param2 param3>;
    do "$latexmlc";
}

but that would need a slightly larger rewrite of the Test.pm setup

[brucemiller]

Sounds good, let's give it a try