Add indexing for the mimetype term

This adds the indexing support for the "mimetype:" term and removes
the broken test flag.  The indexing is probablistic in Xapian terms,
which gives a better experience to end users.  Standard content-types
of the form "foo/bar" are automatically interpreted as phrases in
Xapian due to the embedded slash.

Assume, separate messages with application/pdf and application/x-pdf
are indexed, then:

- mimetype:application/x-pdf will find only the application/x-pdf
- mimetype:application/pdf will find only the application/pdf
- mimetype:pdf will find both of the messages

1 files changed, 1 insertions, 0 deletions

diff --git a/lib/database.cc b/lib/database.cc
index 0d2c4172..3974e2ed 100644
--- a/lib/database.cc
+++ b/lib/database.cc
@@ -254,6 +254,7 @@ static prefix_t PROBABILISTIC_PREFIX[]= {
     { "from",			"XFROM" },
     { "to",			"XTO" },
     { "attachment",		"XATTACHMENT" },
+    { "mimetype",		"XMIMETYPE"},
     { "subject",		"XSUBJECT"},
 };