MSBuild Task: a file "cobra" in the project directory causes and error on Windows.

[thriwkin]

- On Windows,
- running "msbuild.exe" or "xbuild.exe" fails
- with a correct "X.cobraproj" and
- a file "cobra" in the same directory or in a subdirectory "bin".

msbuild /t:Rebuild  X.cobraproj
==>
...Cobra.targets(149,3): error MSB6003: 
    The specified task executable "cobra" could not be run. 
    The specified executable is not a valid application for this OS platform. [...X.cobraproj]

xbuild /t:Rebuild  X.cobraproj
==>
...Cobra.targets: error : 
    Error executing tool '...cobra': 
        ApplicationName='...cobra', 
        CommandLine=...
        CurrentDirectory=...
        Native error= %1
    is not a valid Win32 application. 

Reproduction:
An example of this scenario:
The directory "Source" of the Cobra compiler source (svn-3116)
contains
- the "cobra.cobraproj" file
- and the file "cobra", a bash script.

A "Rebuild" command, given in the Cobra IDE or on the commandline

msbuild /t:Rebuild  cobra.cobraproj

produces 2 failures:
First it fails because the .cobraproj file does not contain any assembly reference
-- see ticket:371
After having inserted an assembly reference,
it fails because the directory of the "cobra.cobraproj" file contains the file "cobra".
Moving the file "cobra" into a subdirectory "bin" does not help.
After having renamed this file, e.g to "(cobra)", all works well.

[thriwkin]

The failure is caused by the MSBuild Task:

# file "CobraCompiler.cobra" in dir "Cobra.MSBuild"
class CobraCompiler ...
    def generateFullPathToTool as String? is protected, override
        cmd = CobraCommand.find     ## <=== 
        if cmd <> nil
            return cmd.path    ## <=== 
            ...

# file "CobraCommand.cobra", in dir "Cobra.Core"
class CobraCommand
    ...
    def _find(path as String, firstTime as bool) as String?
        ...
        else if Directory.exists(path)
            exts = ['', '.cmd', '.bat', '.exe']    ## <=== 
            ...

Possible fix:

        ...
        else if Directory.exists(path)
            if CobraCore.isRunningOnWindows
                exts = ['.cmd', '.bat', '.exe']
            else
                exts = ...