phases: move root phase assignment to it's own function
This moves the initial root phase assignment to it's own function. Future
patches which make phase calculations lazy will use this function to pre-fill
certain phases which can be deduced from the roots.
Test the CIA extension
$ cat >> $HGRCPATH <<EOF
> [extensions]
> hgcia=
>
> [hooks]
> changegroup.cia = python:hgext.hgcia.hook
>
> [web]
> baseurl = http://hgserver/
>
> [cia]
> user = testuser
> project = testproject
> test = True
> EOF
$ hg init src
$ hg init cia
$ cd src
$ echo foo > foo
$ hg ci -Amfoo
adding foo
$ hg push ../cia
pushing to ../cia
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
<message>
<generator>
<name>Mercurial (hgcia)</name>
<version>0.1</version>
<url>http://hg.kublai.com/mercurial/hgcia</url>
<user>testuser</user>
</generator>
<source>
<project>testproject</project>
<branch>default</branch>
</source>
<body>
<commit>
<author>test</author>
<version>0:e63c23eaa88a</version>
<log>foo</log>
<url>http://hgserver/rev/e63c23eaa88a</url>
<files><file uri="http://hgserver/file/e63c23eaa88a/foo" action="add">foo</file></files>
</commit>
</body>
<timestamp>0</timestamp>
</message>
$ cat >> $HGRCPATH <<EOF
> strip = 0
> EOF
$ echo bar > bar
$ hg ci -Ambar
adding bar
$ hg push ../cia
pushing to ../cia
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
<message>
<generator>
<name>Mercurial (hgcia)</name>
<version>0.1</version>
<url>http://hg.kublai.com/mercurial/hgcia</url>
<user>testuser</user>
</generator>
<source>
<project>testproject</project>
<branch>default</branch>
</source>
<body>
<commit>
<author>test</author>
<version>1:c0c7cf58edc5</version>
<log>bar</log>
<url>http://hgserver/$TESTTMP/cia/rev/c0c7cf58edc5</url>
<files><file uri="http://hgserver/$TESTTMP/cia/file/c0c7cf58edc5/bar" action="add">bar</file></files>
</commit>
</body>
<timestamp>0</timestamp>
</message>
$ cd ..