Documentation: use [verse] for SYNOPSIS sections

Documentation: use [verse] for SYNOPSIS sections

The SYNOPSIS sections of most commands that span several lines already
use [verse] to retain line breaks. Most commands that don't span
several lines seem not to use [verse]. In the HTML output, [verse]
does not only preserve line breaks, but also makes the section
indented, which causes a slight inconsistency between commands that
use [verse] and those that don't. Use [verse] in all SYNOPSIS sections
for consistency.

Also remove the blank lines from git-fetch.txt and git-rebase.txt to
align with the other man pages. In the case of git-rebase.txt, which
already uses [verse], the blank line makes the [verse] not apply to
the last line, so removing the blank line also makes the formatting
within the document more consistent.

While at it, add single quotes to 'git cvsimport' for consistency with
other commands.

Signed-off-by: Martin von Zweigbergk <martin.von.zweigbergk@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>