Add option to ignore files in libinterpose

Jens asked if we can add a PATH-like variable for ignoring file accesses in libinterpose. Something like:

KICKSTART_TRACE_IGNORE=/path/to/a:/path/to/b

Or with wildcards:

KICKSTART_TRACE_IGNORE=*.pl:*.pm:*.py:/path/to/foo/*

Which could be implemented with fnmatch()