Support /proc in _dbus_file_get_content
procfs has special semantics: most files are 0 size, only one read can be done on a file, and they are not larger than 4MB. Enhance _dbus_file_get_content() so that we can read files from /proc with it.
Signed-off-by: Luca Boccassi bluca@debian.org
Split out of !398 (merged)