Maxutil: BlitzMaxPath scans CurrentDir for BMK too

- changed BlitzMaxPath() to scan AppDir and CurrentDir, this allows BMK to be a symlinked binary
- kept "path + bin/bmk" to avoid registering the CurrentDir() as BlitzMax path just because it contains a "bmk[.exe]" file. Maybe it is better to check for more than just "this file" to accept it as "BlitzMax"-Path)


@woollybah 
Feel free to NOT accept this pull request - it is not needed for everyone (but you know, cleaner working directories might help during development). If you want to have the ability to run "bmk makemods" from your individual directory, while the environment variable is set to another BlitzMax-directory then we should change order of checks to this:

- currentDir
- environment
- appDir

So we could run it from our individual directory without modifying system wide variables or other things.