Add emerge as pisi history operation

pisi/api.py

@@ -600,6 +600,7 @@ def upgrade(*args, **kw):
     return pisi.operations.upgrade.upgrade(*args, **kw)
 
 def emerge(*args, **kw):
+    pisi.db.historydb.HistoryDB().create_history("emerge")
     return pisi.operations.emerge.emerge(*args, **kw)
 
 def calculate_conflicts(*args, **kw):

pisi/history.py

@@ -76,7 +76,7 @@ class History(xmlfile.XmlFile):
 
     def create(self, operation):
 
-        if operation not in ["upgrade", "remove", "install", "snapshot"]:
+        if operation not in ["upgrade", "remove", "emerge", "install", "snapshot"]:
             raise Exception("Unknown package operation")
         
         self.histfile = "%s_%s.xml" % (self._get_latest(), operation)