Fix path so gphelp will work.

Index: doc/gphelp.in
--- doc/gphelp.in.orig
+++ doc/gphelp.in
@@ -125,7 +125,7 @@ sub get_docdir {
     # work from TOPDIR/Oarch or TOPDIR too: may be uninstalled yet;
     $d = $0; $d =~ s,/gphelp,,;
     for ("$datadir", '.', '..', $d) {
-      my $t = "$_/doc";
+      my $t = "$_/share/doc/pari";
       if (-f "$t/translations") { $d = $t; last; }
     }
     $d ||= "$datadir/doc";	# Last resort