Add some basic branch name tests

tests/test-newbranch

@@ -0,0 +1,26 b''
+#!/bin/sh
+
+hg init t
+cd t
+
+echo foo > a
+hg add a
+hg ci -m "initial" -d "0 0"
+echo foo > .hg/branch
+hg ci -m "add branch name" -d "0 0"
+echo bar > .hg/branch
+hg ci -m "change branch name" -d "0 0"
+rm .hg/branch
+hg ci -m "clear branch name" -d "0 0"
+
+hg co foo
+cat .hg/branch
+echo bleah > a
+hg ci -m "modify a branch" -d "0 0"
+
+hg merge
+cat .hg/branch
+HG_MERGE=true hg ci -m "merge" -d "0 0"
+hg log
+
+

tests/test-newbranch.out

@@ -0,0 +1,43 b''
+0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+foo
+0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+(branch merge, don't forget to commit)
+foo
+changeset:   5:dc140083783b
+branch:      foo
+tag:         tip
+parent:      4:98d14f698afe
+parent:      3:9d567d0b51f9
+user:        test
+date:        Thu Jan 01 00:00:00 1970 +0000
+summary:     merge
+
+changeset:   4:98d14f698afe
+branch:      foo
+parent:      1:0079f24813e2
+user:        test
+date:        Thu Jan 01 00:00:00 1970 +0000
+summary:     modify a branch
+
+changeset:   3:9d567d0b51f9
+user:        test
+date:        Thu Jan 01 00:00:00 1970 +0000
+summary:     clear branch name
+
+changeset:   2:ed2bbf4e0102
+branch:      bar
+user:        test
+date:        Thu Jan 01 00:00:00 1970 +0000
+summary:     change branch name
+
+changeset:   1:0079f24813e2
+branch:      foo
+user:        test
+date:        Thu Jan 01 00:00:00 1970 +0000
+summary:     add branch name
+
+changeset:   0:db01e8ea3388
+user:        test
+date:        Thu Jan 01 00:00:00 1970 +0000
+summary:     initial
+