Symlink downloaded artifacts

[manics]

For example:

• omego download py behaves as normal
• omego download py --sym auto symlinks the unzipped download to OMERO.py
• omego download py --sym /tmp/abc symlinks the unzipped download to /tmp/abc

Closes #60

Changes (since 2017-03-09):

• the default OMERO-CURRENT sym has been changed to OMERO.server, though omego will warn if the old sym is detected.
• rebased
• travis fixed

[joshmoore]

NB: while we're here, should we go ahead and change OMERO-CURRENT to OMERO.server? (That's what you've been doing elsewhere anyway)

cc: @kennethgillen @sbesson

[sbesson]

Assuming our roadmap is 0.5.0, changing the default to OMERO.server makes complete sense to me.

[manics]

Do you think that should be a separate PR (since it's clearly a breaking change)?

[manics]

Also travis has a new error:

$ psql -c "create user omero with password 'omero';" -U postgres
CREATE ROLE

$ psql -c "create database omero with owner omero;" -U postgres
CREATE DATABASE

$ psql -c "select 1;" -U omero -h localhost omero
 ?column? 
----------
        1
(1 row)

(END)

No output has been received in the last 10m0s, this potentially indicates a stalled build or something wrong with the build itself.
Check the details on how to adjust your build configuration on: https://docs.travis-ci.com/user/common-build-problems/#Build-times-out-because-no-output-was-received

The build has been terminated

[joshmoore]

Travis issue:

The repository at ome/omego was not found.

Closing & re-opening.

[manics]

Discovered and fixed a bug in the creation of symlinks when the artifact has already been downloaded and unzipped. Also fixed a test that was effectively assert True 😄