setup.py: install packagescan before any mercurial modules is imported

Further the installation of packagescan over demandload is moved to the
packagescan module.

I added as well few more comments in the packagescan module to avoid
the wrong use of package scan in the future.

Reason:

mercurial.packagescan acts as fake mercurial.demandload during a py2exe
run.  Unfortunatly the import of mercurial.version in setup.py is done
before mercurial.packagescan is installed. This results in few imports
without mercurial.packagescan in charge and therefore not all dependend
modules are detected when running mercurial.packagescan.getmodules
later e.g.  winerror is missed.

mercurial/packagescan.py

@@ -1,5 +1,6 b''
 # packagescan.py - Helper module for identifing used modules.
 # Used for the py2exe distutil.
+# This module must be the first mercurial module imported in setup.py
 #
 # Copyright 2005 Volker Kleinfeld <[e-mail]>
 #
@@ -8,10 +9,16 b''
 import glob
 import os
 import sys
-import demandload
 import ihooks
 
-requiredmodules = {} # Will contain the modules imported by demandload
+# Install this module as fake demandload module
+sys.modules['mercurial.demandload'] = sys.modules[__name__]
+
+# Requiredmodules contains the modules imported by demandload.
+# Please note that demandload can be invoked before the 
+# mercurial.packagescan.scan method is invoked in case a mercurial
+# module is imported.
+requiredmodules = {} 
 def demandload(scope, modules):
     """ fake demandload function that collects the required modules """
     for m in modules.split():
@@ -26,7 +33,7 b' def demandload(scope, modules):'
         scope[module] = mod
         requiredmodules[mod.__name__] = 1
 
-def getmodules(libpath,packagename):
+def scan(libpath,packagename):
     """ helper for finding all required modules of package <packagename> """
     # Use the package in the build directory
     libpath = os.path.abspath(libpath)
@@ -45,8 +52,6 b' def getmodules(libpath,packagename):'
     pymodulefiles = glob.glob('*.py')
     extmodulefiles = glob.glob('*.pyd')
     os.chdir(cwd)
-    # Install a fake demandload module
-    sys.modules['mercurial.demandload'] = sys.modules['mercurial.packagescan']
     # Import all python modules and by that run the fake demandload
     for m in pymodulefiles:
         if m == '__init__.py': continue
@@ -62,8 +67,9 b' def getmodules(libpath,packagename):'
         fullname = packagename+'.'+mname
         __import__(fullname,tmp,tmp)
         requiredmodules[fullname] = 1
-    includes = requiredmodules.keys()
-    return includes
+
+def getmodules():
+    return requiredmodules.keys()
 
 def importfrom(filename):
     """

setup.py

@@ -13,6 +13,8 b' import glob'
 from distutils.core import setup, Extension
 from distutils.command.install_data import install_data
 
+# mercurial.packagescan must be the first mercurial module imported
+import mercurial.packagescan
 import mercurial.version
 
 # py2exe needs to be installed to work
@@ -36,7 +38,6 b' try:'
     # Due to the use of demandload py2exe is not finding the modules.
     # packagescan.getmodules creates a list of modules included in
     # the mercurial package plus depdent modules.
-    import mercurial.packagescan
     from py2exe.build_exe import py2exe as build_exe
 
     class py2exe_for_demandload(build_exe):
@@ -54,10 +55,9 b' try:'
                 self.includes = []
             else:
                 self.includes = self.includes.split(',')
-            self.includes += mercurial.packagescan.getmodules(self.build_lib,
-                                                              'mercurial')
-            self.includes += mercurial.packagescan.getmodules(self.build_lib,
-                                                              'hgext')
+            mercurial.packagescan.scan(self.build_lib,'mercurial')
+            mercurial.packagescan.scan(self.build_lib,'hgext')
+            self.includes += mercurial.packagescan.getmodules()
             build_exe.finalize_options(self)
 except ImportError:
     py2exe_for_demandload = None