win32: read system rcpath from registry

Using the module name was not always helpful.  It breaks down
when Mercurial is installed as source and when the Mercurial
libs are used by external applications.

This patch allows Mercurial installers to store the system wide
rcpath in the registry, where it can always be found.  HGRCPATH
is a poor option for storing the system wide rcpath, since it
overrides both the system and user rcpaths.

doc/hgrc.5.txt

@@ -17,7 +17,9 b' FILES'
 
 Mercurial reads configuration data from several files, if they exist.
 The names of these files depend on the system on which Mercurial is
-installed.
+installed. Windows registry keys contain PATH-like strings, every
+part must reference a Mercurial.ini file or be a directory where *.rc
+files will be read.
 
 (Unix)    <install-root>/etc/mercurial/hgrc.d/*.rc::
 (Unix)    <install-root>/etc/mercurial/hgrc::
@@ -29,6 +31,8 b' installed.'
 
 (Unix)    /etc/mercurial/hgrc.d/*.rc::
 (Unix)    /etc/mercurial/hgrc::
+(Windows) HKEY_LOCAL_MACHINE\SOFTWARE\Mercurial::
+  or::
 (Windows) C:\Mercurial\Mercurial.ini::
     Per-system configuration files, for the system on which Mercurial
     is running.  Options in these files apply to all Mercurial

mercurial/util_win32.py

@@ -16,6 +16,7 b' import win32api'
 from i18n import _
 import errno, os, pywintypes, win32con, win32file, win32process
 import cStringIO, winerror
+import osutil
 from win32com.shell import shell,shellcon
 
 class WinError:
@@ -179,6 +180,20 b' def testpid(pid):'
 
 def system_rcpath_win32():
     '''return default os-specific hgrc search path'''
+    try:
+        value = win32api.RegQueryValue(
+                win32con.HKEY_LOCAL_MACHINE, 'SOFTWARE\\Mercurial')
+        rcpath = []
+        for p in value.split(os.pathsep):
+            if p.lower().endswith('mercurial.ini'):
+                rcpath.append(p)
+            elif os.path.isdir(p):
+                for f, kind in osutil.listdir(p):
+                    if f.endswith('.rc'):
+                        rcpath.append(os.path.join(p, f))
+        return rcpath
+    except pywintypes.error:
+        pass
     proc = win32api.GetCurrentProcess()
     try:
         # This will fail on windows < NT