Pathnames beginning with more than one slash cause invalid output

[da-x]

If we pass pathnames starting with more than one slash to -include, cpphs generates invalid output. These are valid UNIX pathnames. I've tested with version 1.20.1 on Linux.

Example:

$ touch empty.hs
$ cpphs --cpp -include //dev/null empty.hs
#line 1 "test.hs"
#line 1 "
#line 2 "test.hs"
#line 1 "test.hs"

If I remove the extra '/', I get a good output:

$ touch empty.hs
$ cpphs --cpp -include /dev/null empty.hs
#line 1 "test.hs"
#line 1 "/dev/null"
#line 2 "test.hs"
#line 1 "test.hs"