Allow to validate the config file without X.

We're going to call parse_configuration() very early if -C is given on
the command line. Instead of the previous "only_check_config", which has
been a global variable, we now simply pass use_nagbar as false if we're
just validating.

This causes the whole parsing to run without X and of course without
starting nagbar and displaying the errors to standard out/error instead.

The return code of parse_configuration() is now a boolean which
represents whether an error occured during parsing and the programs exit
code is returned accordingly.

Although the config parser still has a lot of side-effects, we now can
parse without the need to have an XCB connection. A nicer implementation
would be to just set the new font and load it just after we're done
parsing, but to ensure we don't break functionality we just load a dummy
FONT_TYPE_NONE if XCB isn't available. The main reason for going this
route is that it's a bit difficult to test fonts in a distribution
agnostic way without bundling fonts with i3 (or Xdummy to be more
exact).

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

include/config.h

@@ -326,6 +326,20 @@ struct Barconfig {
     TAILQ_ENTRY(Barconfig) configs;
 };
 
+/**
+ * Finds the configuration file to use (either the one specified by
+ * override_configpath), the user’s one or the system default) and calls
+ * parse_file().
+ *
+ * If you specify override_configpath, only this path is used to look for a
+ * configuration file.
+ *
+ * If use_nagbar is false, don't try to start i3-nagbar but log the errors to
+ * stdout/stderr instead.
+ *
+ */
+bool parse_configuration(const char *override_configpath, bool use_nagbar);
+
 /**
  * Reads the configuration from ~/.i3/config or /etc/i3/config if not found.
  *