imap-related bugfixes.

* imap4d/search.c (imap4d_search0): Use parsebuf.err_mesg if defined,
otherwise fall back to the general "parse error" message.
* include/mailutils/datetime.h (MU_DATETIME_INTERNALDATE): Use %e for
day. Day can be one-digit decimal.
* libmailutils/datetime/scantime.c (mu_scan_datetime): Skip initial
ws for %e.
* mu/imap.c (com_search): Print newline after the "no matches" message.