Support compiling ScriptExec on newer versions of OS X (please review)

* packaging/macosx/Resources/script, packaging/macosx/Resources/bin/inkscape: Improve quoting of shell variables. * packaging/macosx/ScriptExec/ScriptExec.xcodeproj/project.pbxproj: Xcode 2 project file for the OS X launcher. This will build a Universal version of the launcher by default. The project files for different versions are named differently, so this will be picked up and used if the package builder has a sufficiently new version of Xcode. * packaging/macosx/ScriptExec/ScriptExec.xcode/sveinbjornt.pbxuser, packaging/macosx/ScriptExec/ScriptExec.xcode/voisine.pbxuser: Remove unnecessary user preference files. * Makefile.am: Update the Xcode project files included when creating releases.