Make python dependencies extraction much faster

New style rpm dependency extractors mean that the script is
called for each file in the package. This exhibit the slowness
of the python one, where most of the time is spent on importing
a module which is usually not needed.

Running pythoneggs.py --requires on python-setuptools:

Before:
real	1m43.763s
user	1m33.220s
sys	0m7.460s

After:
real	0m18.298s
user	0m15.060s
sys	0m2.190s

1 files changed, 2 insertions, 1 deletions

diff --git a/pythoneggs.py b/pythoneggs.py
index 367aad1..a1c819b 100755
--- a/pythoneggs.py
+++ b/pythoneggs.py
@@ -12,7 +12,6 @@
 from getopt import getopt
 from os.path import basename, dirname, isdir, sep, splitext
 from sys import argv, stderr, stdin, version
-from pkg_resources import Distribution, FileMetadata, PathMetadata
 from distutils.sysconfig import get_python_lib
 
 
@@ -82,6 +81,8 @@ for f in files:
             parent_name.endswith('.egg-info') or \
             parent_name.endswith('.egg-link')
     if file_match or dir_match:
+        # This import is very slow, so only do it if needed
+        from pkg_resources import Distribution, FileMetadata, PathMetadata
         dist_name = basename(f)
         if dir_match:
             path_item = dirname(parent_name)