user-manual: Fix 'both: so' -> 'both; so' typo

The clause "so `git log ...` will return no commits..." is
independent, not a description of "both", so a semicolon is more
appropriate.

Signed-off-by: W. Trevor King <wking@tremily.us>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
user-manual: Fix 'http' -> 'HTTP' typos

HTTP is an acronym which has not (yet) made the transition to word
status (unlike "laser", probably because lasers are inherently cooler
than HTTP ;).

Signed-off-by: W. Trevor King <wking@tremily.us>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
user-manual: Fix 'you - Git' -> 'you--Git' typo

Use an em-dash, not a hyphen, to join these clauses.

Signed-off-by: W. Trevor King <wking@tremily.us>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
user-manual: Rewrite git-gc section for automatic packing

This should have happened back in 2007, when `git gc` learned about
auto (e9831e8, git-gc --auto: add documentation, 2007-09-17).

Signed-off-by: W. Trevor King <wking@tremily.us>
Signed-off-by: Junio C Hamano <gitster@pobox.com>