setup.py: skip inotify if there's no inotify_add_watch

Debian Etch doesn't include a sys/inotify.h header, which makes it
impossible to compile _inotify.c, making hg uninstallable.

The cc.has_function() method is implemented by trying to compile a
simple C program.  Since there's no redirection involved all error
messages are sent to the terminal.  This is not particularly pretty
but at least it allows the installation to complete.

setup.py

@@ -1,95 +1,99 b''
 #!/usr/bin/env python
 #
 # This is the mercurial setup script.
 #
 # 'python setup.py install', or
 # 'python setup.py --help' for more options
 
 import sys
 if not hasattr(sys, 'version_info') or sys.version_info < (2, 3, 0, 'final'):
     raise SystemExit, "Mercurial requires python 2.3 or later."
 
 import os
 from distutils.core import setup, Extension
 from distutils.command.install_data import install_data
+from distutils.ccompiler import new_compiler
 
 import mercurial.version
 
 extra = {}
 
 # py2exe needs to be installed to work
 try:
     import py2exe
 
     # Help py2exe to find win32com.shell
     try:
         import modulefinder
         import win32com
         for p in win32com.__path__[1:]: # Take the path to win32comext
             modulefinder.AddPackagePath("win32com", p)
         pn = "win32com.shell"
         __import__(pn)
         m = sys.modules[pn]
         for p in m.__path__[1:]:
             modulefinder.AddPackagePath(pn, p)
     except ImportError:
         pass
 
     extra['console'] = ['hg']
 
 except ImportError:
     pass
 
 # specify version string, otherwise 'hg identify' will be used:
 version = ''
 
 class install_package_data(install_data):
     def finalize_options(self):
         self.set_undefined_options('install',
                                    ('install_lib', 'install_dir'))
         install_data.finalize_options(self)
 
 mercurial.version.remember_version(version)
 cmdclass = {'install_data': install_package_data}
 
 ext_modules=[
     Extension('mercurial.mpatch', ['mercurial/mpatch.c']),
     Extension('mercurial.bdiff', ['mercurial/bdiff.c']),
     Extension('mercurial.base85', ['mercurial/base85.c']),
     Extension('mercurial.diffhelpers', ['mercurial/diffhelpers.c'])
     ]
 
 packages = ['mercurial', 'mercurial.hgweb', 'hgext', 'hgext.convert']
 
 try:
     import posix
     ext_modules.append(Extension('mercurial.osutil', ['mercurial/osutil.c']))
 
     if sys.platform == 'linux2' and os.uname()[2] > '2.6':
-        # the inotify extension is only usable with Linux 2.6 kernels
-        ext_modules.append(Extension('hgext.inotify.linux._inotify',
-                                     ['hgext/inotify/linux/_inotify.c']))
-        packages.extend(['hgext.inotify', 'hgext.inotify.linux'])
+        # The inotify extension is only usable with Linux 2.6 kernels.
+        # You also need a reasonably recent C library.
+        cc = new_compiler()
+        if cc.has_function('inotify_add_watch'):
+            ext_modules.append(Extension('hgext.inotify.linux._inotify',
+                                         ['hgext/inotify/linux/_inotify.c']))
+            packages.extend(['hgext.inotify', 'hgext.inotify.linux'])
 except ImportError:
     pass
 
 setup(name='mercurial',
       version=mercurial.version.get_version(),
       author='Matt Mackall',
       author_email='[e-mail]',
       url='http://selenic.com/mercurial',
       description='Scalable distributed SCM',
       license='GNU GPL',
       scripts=['hg'],
       packages=packages,
       ext_modules=ext_modules,
       data_files=[(os.path.join('mercurial', root),
                    [os.path.join(root, file_) for file_ in files])
                   for root, dirs, files in os.walk('templates')],
       cmdclass=cmdclass,
       options=dict(py2exe=dict(packages=['hgext']),
                    bdist_mpkg=dict(zipdist=True,
                                    license='COPYING',
                                    readme='contrib/macosx/Readme.html',
                                    welcome='contrib/macosx/Welcome.html')),
       **extra)