bug#15461: 24.3; exec-path on ms windows should contain current directory

[Jarek Czekalski <jarekczek@poczta.onet.pl>]

Some analyzis done:

1. shell-command uses libexec\emacs\24.3.50\i686-pc-mingw32\cmdproxy.exe 
and this proxy locates files in the current directory. Side note: it 
ignores exec-path and uses only system PATH variable
2. call-process does not run programs from the current directory (a new bug)

Now the Stefan's suggestion:

> Completion should mirror the behavior of the code that spawns the
> process

, which seemed perfectly at the beginning, makes less sense. Which 
code's behaviour should be copied?

I guess first call-process should be fixed to include the current 
directory, then its behaviour may be copied.

Any suggestions in which direction to go? Maybe the simplest consing 
exec-path is still an option? Should I look at potential problems of 
that solution?

I'm happy that my initial title for the bug makes sense now, because not 
only completion is affected, but the spawning process as well :)

Jarek