[Eric] Relative project path for project files

[Klenongan]

We have this setup here where the project file cannot be saved at the
root of the project directory. It was meant for a single build file (a
Makefile, SConstruct, CMakeLists, or whatever.. with includes/imports
to more files in the "buildsys/" when necessary) and a small textfile
like README.txt describing what the project is, how to build it (what
build system used, dependencies, commands, etc.), contact info. to
people who responsible/maintain this, repository location, location of
files, and so on.

I don't like it but that's the way it is. I've been using (g)vim for
Python for quite sometime, and this "requirements" didn't actually
constrain me because vim just don't care about file locations. But
once I bring eric to the table, I realize that I have to bend either
the IDE (eric) or the rule because it seems eric project file (eg.
project.c4p) expects to be located at the root of the project
directory (http://www.riverbankcomputing.com/pipermail/eric/2010-June/002622.html).

Well, I decided to "bend" eric (ie. because I cant change the rules)
and this is what I came up with:

   https://gist.github.com/2584467

I use a rather ugly "^^PROJECTPATH" key because it's a hack, of course
the preferable name should be pdata["PROJECTPATH"] or something like
that should the author(s) agree to my code.

I hope the author(s) can consider it for adoption.

ps. I'm sorry for any grammatical error(s), English is not my native language.