doc/Makefile: do not include hg.1.gendoc.txt in MANIFEST
It is an intermediate file used to produce the hg.1 and .hg.1.html
files and is not useful for people who download the tarball. It will
be regenerated automatically by the Makefile if users want to rebuild
the documentation.
$ mkdir a
$ cd a
$ hg init
$ echo 123 > a
$ hg add a
$ hg commit -m "a" -u a
$ cd ..
$ mkdir b
$ cd b
$ hg init
$ 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
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
(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