notmuch_message_get_header started returning some headers straight
from the database in
567bcbc, but this comment explicitly claimed all
headers were read from the message file.
/* Get the value of the specified header from 'message'.
*
- * The value will be read from the actual message file, not from the
- * notmuch database. The header name is case insensitive.
+ * Common headers are stored in the database when the message is
+ * indexed and will be returned from the database. Other headers will
+ * be read from the actual message file.
+ *
+ * The header name is case insensitive.
*
* The returned string belongs to the message so should not be
* modified or freed by the caller (nor should it be referenced after