Cutting useless hg head

$ mkdir tmp
$ cd tmp
$ hg init
$ echo "Hello world" > hello1.txt
$ hg add hello1.txt
$ hg ci -m "initial"
$ hg glog
@  changeset:   0:734d0ba76823
   tag:         tip
   user:        Vadim Ippolitov <vadipp@gmail.com>
   date:        Fri Nov 02 15:18:33 2012 +0700
   summary:     initial

$ echo "Hello change1" >
.hg/        hello1.txt
$ echo "Hello change1" > hello1.txt
$ hg ci -m "change1"
$ hg up -r 0  #  go back, try something different
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo "Hello change2" > hello1.txt
$ hg ci -m "change2"
created new head
$ hg glog
@  changeset:   2:cb7537497910
|  tag:         tip
|  parent:      0:734d0ba76823
|  user:        Vadim Ippolitov <vadipp@gmail.com>
|  date:        Fri Nov 02 15:19:54 2012 +0700
|  summary:     change2
|
| o  changeset:   1:d6ec861fcfa0
|/   user:        Vadim Ippolitov <vadipp@gmail.com>
|    date:        Fri Nov 02 15:19:35 2012 +0700
|    summary:     change1
|
o  changeset:   0:734d0ba76823
   user:        Vadim Ippolitov <vadipp@gmail.com>
   date:        Fri Nov 02 15:18:33 2012 +0700
   summary:     initial

$ #Change 1 was a bad idea, change 2 looks bteter
$ hg up -r 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg commit --close-branch -m "change 1 is a bad idea, closing branch"
$ hg up -c 2
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg heads
changeset:   2:cb7537497910
parent:      0:734d0ba76823
user:        Vadim Ippolitov <vadipp@gmail.com>
date:        Fri Nov 02 15:19:54 2012 +0700
summary:     change2

$ hg glog
o  changeset:   3:cbec5fc011be
|  tag:         tip
|  parent:      1:d6ec861fcfa0
|  user:        Vadim Ippolitov <vadipp@gmail.com>
|  date:        Fri Nov 02 15:20:58 2012 +0700
|  summary:     change 1 is a bad idea, closing branch
|
| @  changeset:   2:cb7537497910
| |  parent:      0:734d0ba76823
| |  user:        Vadim Ippolitov <vadipp@gmail.com>
| |  date:        Fri Nov 02 15:19:54 2012 +0700
| |  summary:     change2
| |
o |  changeset:   1:d6ec861fcfa0
|/   user:        Vadim Ippolitov <vadipp@gmail.com>
|    date:        Fri Nov 02 15:19:35 2012 +0700
|    summary:     change1
|
o  changeset:   0:734d0ba76823
   user:        Vadim Ippolitov <vadipp@gmail.com>
   date:        Fri Nov 02 15:18:33 2012 +0700
   summary:     initial

$ hg merge  # if we try to merge, there nothing to merge - the other head was closed
abort: branch 'default' has one head - please merge with an explicit rev
(run 'hg heads' to see all heads)