Feature: Add ability to avoid source packages from building on specific architectures

Example:

<Source>
    <Name>psyco</Name>
    ..
    ..
    <ExcludeArch>x86_64</ExcludeArch>
</Source>

will avoid the package psyco from building on systems where pisi.conf->architecture == x86_64

pisi-spec.rng

@@ -26,6 +26,9 @@
             <ref name="Name"/>
             <ref name="Homepage"/>
             <ref name="Packager"/>
+            <zeroOrMore>
+                <ref name="ExcludeArch">
+            </zeroOrMore>
             <oneOrMore>
                 <ref name="License"/>
             </oneOrMore>

pisi/operations/build.py

@@ -51,6 +51,9 @@ class ActionScriptException(Error):
 class AbandonedFilesException(Error):
     pass
 
+class ExcludedArchitectureException(Error):
+    pass
+
 # Helper Functions
 def get_file_type(path, pinfo_list, install_dir):
     """Return the file type of a path according to the given PathInfo
@@ -241,6 +244,11 @@ class Builder:
     def build(self):
         """Build the package in one shot."""
 
+        architecture = ctx.config.values.general.architecture
+        if architecture in self.spec.source.excludeArch:
+            raise ExcludedArchitectureException(_("pspec.xml avoids this package from building for '%s'") % architecture)
+
+
         ctx.ui.status(_("Building PiSi source package: %s") % self.spec.source.name)
 
         self.compile_action_script()

pisi/specfile.py

@@ -164,6 +164,7 @@ class Source:
     t_Name = [autoxml.String, autoxml.mandatory]
     t_Homepage = [autoxml.String, autoxml.optional]
     t_Packager = [Packager, autoxml.mandatory]
+    t_ExcludeArch = [ [autoxml.String], autoxml.optional]
     t_License = [ [autoxml.String], autoxml.mandatory]
     t_IsA = [ [autoxml.String], autoxml.optional]
     t_PartOf = [autoxml.String, autoxml.optional]