[PATCH] Simplify commit and tag parsing

[John Keeping]

On Thu, Mar 05, 2015 at 11:46:55AM +0100, Jason A. Donenfeld wrote:
> This commit breaks ui-tag. The first few lines of tag messages are cut off.

It looks like parse_user() consumes the trailing LF on the user line, so
next_header_line() ends up skipping the blank line at the end of the
header.

I suspect the right answer is to stop parse_user() eating the LF since
all of the call sites go through next_header_line() after this patch.