DOCS: Corrected IMAP URL examples according to RFC5092

URL examples that included the UID weren't technically correct although
would pass the curl parser.
imap: Fixed incorrect comparison for STARTTLS in imap_endofresp()

Corrected the comparison type in addition to commit 1dac29fa83a9.
imap: Minor tidy up of comments in imap_parse_url_path()

Tidy up of comments before next round of imap changes.