hgweb: make followlines button absolutely positioned
It used to have position: absolute only on annotate page, but it makes sense to
have it everywhere, because the button shouldn't affect other elements at all.
Especially since the button has a set height, which meant that for certain
smaller fonts source lines were changing their height on hover.
Note that the button doesn't set any of the usual properties that accompany
absolute position (top, right, bottom or left). These properties would position
the button without any account for source line padding. Instead, margins are
used (the button already has all margins defined, they do the job).
$ hg init a
$ cd a
$ echo 123 > a
$ hg add a
$ hg commit -m "a" -u a
$ cd ..
$ hg init b
$ cd b
$ echo 321 > b
$ hg add b
$ hg commit -m "b" -u b
$ hg pull ../a
pulling from ../a
searching for changes
abort: repository is unrelated
[255]
$ hg pull -f ../a
pulling from ../a
searching for changes
warning: repository is unrelated
requesting all changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
new changesets 9a79c33a9db3
(run 'hg heads' to see heads, 'hg merge' to merge)
$ hg heads
changeset: 1:9a79c33a9db3
tag: tip
parent: -1:000000000000
user: a
date: Thu Jan 01 00:00:00 1970 +0000
summary: a
changeset: 0:01f8062b2de5
user: b
date: Thu Jan 01 00:00:00 1970 +0000
summary: b
$ cd ..