- Fix cmd's SearchForExecutable: it was inside out, giving extension priority over...

- Fix cmd's SearchForExecutable: it was inside out, giving extension priority over directory.
- Remove code that checked if the file's extension was in PATHEXT. Windows does not check, and it's very handy to be able to "run" non-executable files.
- Allow explicit paths with no backslash (like "A:file")
- Batch: use GetFullPathName to get the batch file's absolute path; this way %~dp0 will always give the right directory even in the weird case of running the .bat via a relative path in PATH. Remove code in SearchForExecutable which tried to make sure it returned an absolute path (but it didn't in that case).

svn path=/trunk/; revision=35187