write test cases for compose_rev()
write interface and implementations for compose_rev()
fill out docstring of canonical_rev()

This is to clear up the difference between compose_rev() and canonical_rev().
Merge pull request #56 from OEP/feature/compose-rev

Test cases and implementation for compose_rev() operation
add test methods for proplist
fix SvnRepo.proplist() for Subversion 1.8+ (issue #51)
factor out VCSRepo._command into function

Use this instead of depending on subprocess.check_output() in anyvcs/svn.py
Merge branch 'develop' into feature/issue/51

Conflicts:
	tests.py
Merge pull request #57 from OEP/feature/issue/51

Fix SvnRepo.proplist() for Subversion 1.8+ (issue #51)
Merge branch 'develop' into feature/svn-fast-path-diff

Conflicts:
	anyvcs/svn.py