Fix diagnose::check_permissions for rsync sources

Closes: https://trac.macports.org/ticket/69126
(cherry picked from commit f37bf45)

src/macports1.0/diagnose.tcl

@@ -799,7 +799,7 @@ namespace eval diagnose {
  # don't complain about writable parent dirs of prefix or sources
  set check_paths [list [file dirname $macports::prefix]]
  foreach source $macports::sources {
- set sourcedir [macports::getportdir [lindex $source 0]]
+ set sourcedir [file dirname [macports::getindex [lindex $source 0]]]
  if {$sourcedir ni $check_paths} {
  lappend check_paths $sourcedir
  }