Test that we have an executable *file*

Fixes #939

Author: Ivoz

virtualenv.py

@@ -1547,6 +1547,7 @@ def resolve_interpreter(exe):
     """
     # If the "executable" is a version number, get the installed executable for
     # that version
+    orig_exe = exe
     python_versions = get_installed_pythons()
     if exe in python_versions:
         exe = python_versions[exe]
@@ -1558,16 +1559,16 @@ def resolve_interpreter(exe):
                 exe = join(path, exe)
                 break
     if not os.path.exists(exe):
-        logger.fatal('The executable %s (from --python=%s) does not exist' % (exe, exe))
+        logger.fatal('The path %s (from --python=%s) does not exist' % (exe, orig_exe))
         raise SystemExit(3)
     if not is_executable(exe):
-        logger.fatal('The executable %s (from --python=%s) is not executable' % (exe, exe))
+        logger.fatal('The path %s (from --python=%s) is not an executable file' % (exe, orig_exe))
         raise SystemExit(3)
     return exe
 
 def is_executable(exe):
     """Checks a file is executable"""
-    return os.access(exe, os.X_OK)
+    return os.path.isfile(exe) and os.access(exe, os.X_OK)
 
 ############################################################
 ## Relocating the environment: