Windows fixes

- Use pipes "|"
 - Improved system command, create a temporary .sh faile that is executed  with cygwins sh(bash)
   This makes the Windows version behave exactly as the Lunix version(well almost...) 
 - Give unix path to DBUG, trace files is no produced if running ./mysql-test-run.pl --debug"


client/mysqltest.c:
  Add new function "my_system" that run the <command> a she script using cygwin bash on windows.
mysql-test/lib/mtr_misc.pl:
  Return all paths to executables in windows format "c:\src\.." when run on windows.
  This makes it possible to use the pipes "|" to pipöe the output form exeample "mysqlbinlog" into "mysql"
mysql-test/mysql-test-run.pl:
  DBUG want's a unix format strings for where it should put the tracefile(don't ask me why but it works)
  Just chop of the first "c:" from the "c:/src/.." string and DBUG will be happy

mysql-test/mysql-test-run.pl

@@ -668,6 +668,9 @@ sub command_line_setup () {
     $opt_vardir= "$glob_mysql_test_dir/var";
   }
   $opt_vardir_trace= $opt_vardir;
+  # Chop off any "c:", DBUG likes a unix path ex: c:/src/... => /src/...
+  $opt_vardir_trace=~ s/^\w://;
+
   # We make the path absolute, as the server will do a chdir() before usage
   unless ( $opt_vardir =~ m,^/, or
            ($glob_win32 and $opt_vardir =~ m,^[a-z]:/,i) )