Avoid sorting the working set and requirements when it won't be logged.

Backport 124059 from trunk.

CHANGES.txt

@@ -4,6 +4,13 @@ Change History
 1.4.5 (unreleased)
 ==================
 
+- Avoid sorting the working set and requirements when it won't be
+  logged.  When profiling a simple buildout with 10 parts with
+  identical and large working sets, this resulted in a decrease of run
+  time from 93.411 to 15.068 seconds, about a 6 fold improvement.  To
+  see the benefit be sure to run without any increase in verbosity
+  ("-v" option).  (rossp)
+
 - Introduce a cache for the expensive `buildout._dir_hash` function.
 
 - Remove duplicate path from script's sys.path setup.

src/zc/buildout/easy_install.py

@@ -1200,6 +1200,15 @@ def __str__(self):
         return "Couldn't find a distribution for %r." % str(req)
 
 def _log_requirement(ws, req):
+    if not logger.isEnabledFor(logging.DEBUG):
+        # Sorting the working set and iterating over it's requirements
+        # is expensive, so short cirtuit the work if it won't even be
+        # logged.  When profiling a simple buildout with 10 parts with
+        # identical and large working sets, this resulted in a
+        # decrease of run time from 93.411 to 15.068 seconds, about a
+        # 6 fold improvement.
+        return
+
     ws = list(ws)
     ws.sort()
     for dist in ws: