Bug#787575: pysph: FTBFS w/o writable home directory

[Aaron M. Ucko]

Source: pysph
Version: 0~20141130.git9132872-1
Severity: serious
Justification: fails to build from source

Builds of pysph in environments (notably, on the autobuilders) lacking
writable home directories have been failing when trying to run tests
(assuming they get past #787573):

    File "/«PKGBUILDDIR»/pysph/sph/sph_compiler.py", line 26, in compile
      self.ext_mod = ExtModule(code, verbose=True)
    File "/«PKGBUILDDIR»/pysph/base/ext_module.py", line 42, in __init__
      self._setup_root(root)
    File "/«PKGBUILDDIR»/pysph/base/ext_module.py", line 96, in _setup_root
      os.makedirs(self.build_dir)
    File "/usr/lib/python2.7/os.py", line 150, in makedirs
      makedirs(head, mode)
    File "/usr/lib/python2.7/os.py", line 150, in makedirs
      makedirs(head, mode)
    File "/usr/lib/python2.7/os.py", line 150, in makedirs
      makedirs(head, mode)
    File "/usr/lib/python2.7/os.py", line 157, in makedirs
      mkdir(name, mode)
  OSError: [Errno 13] Permission denied: '/sbuild-nonexistent'

The code in question does at least appear to honor HOME, so it should
suffice to arrange to run tests with HOME set to a directory within
the build tree and for debian/rules clean to wipe that directory out.

Could you please take a look?

Thanks!