ESource: Use a collation key for display name comparisons.
ESource: Use a collation key for display name comparisons.

e_source_compare_by_display_name() gets called a lot.  We've been
calling g_utf8_collate() each time, which is known to be slow when
comparing large numbers of UTF-8 strings.

We now stash a collation key during e_source_set_display_name()
by passing the UTF-8 display name to g_utf8_collate_key().  Then
in e_source_compare_by_display_name() we can simply call strcmp()
on the internal collation keys to compare display names.

Didn't take any real performance measurements other than seeing
e_source_compare_by_display_name() topping the charts in sysprof.

Distrotech/evolution-data-server,Distrotech/evolution-data-server,matzipan/evolution-data-server,Distrotech/evolution-data-server,Distrotech/evolution-data-server,matzipan/evolution-data-server,tintou/evolution-data-server,matzipan/evolution-data-server,tintou/evolution-data-server,matzipan/evolution-data-server,tintou/evolution-data-server,matzipan/evolution-data-server,tintou/evolution-data-server,Distrotech/evolution-data-server