The patch adds support for a new tag in AppInfo.xml:
<AppDirVar>. If present it should contain the name of a
variable which will be set to the path of the AppDir.
This variable will be set within the filer so that any
subprocess of the filer can access it.
The variable will, currently, only be set on running
the AppDir but a one line addition in
diritem.c->examine_dir() can enable it for the var to
be set on just looking at an AppDir. In this case, the
"overwrite" parameter to filer_boot() would be set to 0.
This will mostly be of use to AppDirs containing
modules for use by other programs, or include files etc.