chgserver: add [alias] to confighash

The [alias] config section affects a global state: commands.table. It's hard
to trace whether an alias is added by a config option or an extension, and
add/remove aliases in a safe way per chg request. It will hurt performance a
bit if we clean the table and parse aliases every time. Therefore let's just
add it to confighash.

This will make chg pass test-pager.t.

hgext/chgserver.py

@@ -80,6 +80,7 b' def _hashlist(items):'
 
 # sensitive config sections affecting confighash
 _configsections = [
+    'alias',  # affects global state commands.table
     'extdiff',  # uisetup will register new commands
     'extensions',
 ]