Procedure

Old:

[lethe] mercurial-1.7.3% sudo make PREFIX=/util/mercurial-1.7.3 install
[lethe] mercurial-1.7.3% cd /util
[lethe] /util% sudo rm mercurial
[lethe] /util% sudo ln -s mercurial-1.7.3 mercurial
[lethe] /util% cd /util/bin
[lethe] bin% sudo ln -s ../mercurial/bin/hg hg

New:

[lethe] ~% cd /src/util/mercurial-2.5.2

Edit Makefile, change:

PYTHON=python

to

PYTHON=python2.7
PURE=--pure

[lethe] mercurial-2.5.2% sudo make PREFIX=/util/mercurial-2.5.2 install
[lethe] mercurial-2.5.2% cd /util
[lethe] /util% sudo rm mercurial
[lethe] /util% sudo ln -s mercurial-2.5.2 mercurial
[lethe] /util% cd /util/bin
[lethe] bin% sudo ln -s ../mercurial/bin/hg hg

Notes

1. As of March 2013, Mercurial has no plans to support Python 3.x. So continue to build Mercurial with Python 2.7.

References

1. http://mercurial.selenic.com/wiki/SupportedPythonVersions