Allow IPv6 host addresses

Syntax examples:
  fe80::1111:2222:3333:4444
  user@fe80::1
  user@[::1]:2222 (square brackets are necessary for non-standard ssh port number)
Add IPv6 support for rsync project synchronization
Add some IPv6 related comments
Add test coverage for IPv6 related functions
fix typo
Change `ssh` agent forward class & close when done

Fixes #562
Merge branch '1.4'
Cut 1.3.7
Merge branch '1.3' into 1.4

Conflicts:
	docs/changelog.rst
	fabric/version.py
Cut 1.4.2
Merge branch '1.4'

Conflicts:
	fabric/version.py
Docs, unused env var added in prep for #633
Straighten up host/role merge tests to explicitly test deduping
@patched_env was horribly broken and unnecessary uggggggggh
Test and implementation
Changelog re #633
Typo fix
Add quiet contextmanager and run/sudo kwarg.

Fixes #627.
Roadmap update
Clarify relative root file path of lcd().

Fixes #634