Add robust test suite for mdconvert. A few bugs in the library were identified and fixed, including incorrect handling on stride when n_frames was supplied in binpos, xtc and trr, a crash in hdf5 when mutliple chunks were read with striding, updating mdconvert to use the new topology subsetting function, bug in binpos involving multiple writes to the same file not being registered correctly, and moved the test suite from mdtraj.test to mdtraj.tests, because now there's a new function mdtraj.test() that runs nose. this is nice because you can run it from another directory besides the source directory

Close rmcgibbo/mdtraj#107

Squashed commit of the following:

commit eb0b99c7a1c3f589d5b83938d67d30ab18baa6b9
Author: Robert McGibbon <rmcgibbo@gmail.com>
Date:   Sun Jun 30 03:32:22 2013 -0700

    update .travis for tests being in a directory with a plural

commit 89e85bc82437bc0ef539156f54b9c5e4b854b971
Author: Robert McGibbon <rmcgibbo@gmail.com>
Date:   Sun Jun 30 03:30:27 2013 -0700

    moved complexity out of __init__ and into a new file in testing

commit 162cf5d32fbaf0e83110777337cef1467281eeec
Author: Robert McGibbon <rmcgibbo@gmail.com>
Date:   Sun Jun 30 03:10:50 2013 -0700

    moved test directory from test/ to tests/, which is how it is in numpy. this lets us have a function in __init__ called test()'

commit 384cb78d0f0f19b27b9b1eec04aeb08385d5ad5f
Author: Robert McGibbon <rmcgibbo@gmail.com>
Date:   Sun Jun 30 01:41:36 2013 -0700

    fix bug in hdf5.py where the frame_index was beng advanced too far

commit 6005aed3ffd9f1771ac3b390a948e3edcb359da9
Author: Robert McGibbon <rmcgibbo@gmail.com>
Date:   Sun Jun 30 01:37:06 2013 -0700

    add scripttest to the delay_import code, so that we can run the test_mdconvert on machines without it installed

commit 836086723ea4ffe4cff15f536f5627ea949df997
Author: Robert McGibbon <rmcgibbo@gmail.com>
Date:   Sun Jun 30 01:35:51 2013 -0700

    make testing.eq() return true so that it can be chained in a single statement

commit 1e4a81ee9fc0862849bf1de86d7438dbee118731
Author: Robert McGibbon <rmcgibbo@gmail.com>
Date:   Sun Jun 30 01:34:47 2013 -0700

    oops. forgot to add the binpos test too

commit daa537ff9ed4da3bf9f77159d9c0f0aa2869a470
Author: Robert McGibbon <rmcgibbo@gmail.com>
Date:   Sun Jun 30 01:34:28 2013 -0700

    the c code too

commit e5a09e577f221c4371618d61616a370d669305db
Author: Robert McGibbon <rmcgibbo@gmail.com>
Date:   Sun Jun 30 01:34:06 2013 -0700

    add tests to check for bug that previous commit fixed

commit acfe78d2fcb808984d48089cc9afceabacdfd766
Author: Robert McGibbon <rmcgibbo@gmail.com>
Date:   Sun Jun 30 01:33:27 2013 -0700

    add fixes for n_frames/stride simultanious bug

commit d9b2d5d663fd14b5189e2a70ebcc9d062af381df
Author: Robert McGibbon <rmcgibbo@gmail.com>
Date:   Sun Jun 30 01:10:55 2013 -0700

    update mdconvert to use new topology subsetting

commit 12dfb50fa62549e620ad86505ebfef296b1eb6f8
Author: Robert McGibbon <rmcgibbo@gmail.com>
Date:   Sat Jun 29 23:06:41 2013 -0700

    Changed mdconvert test w.r.t. chunking and found a serios bug in save_binpos when multiple writes occured on the same file. fixed bug and added a tests to the test_binpos suite to catch it

commit 278dab7721fefb278bedc3f3d7797eab799caf04
Author: Robert McGibbon <rmcgibbo@gmail.com>
Date:   Sat Jun 29 22:56:04 2013 -0700

    add installation of the dependecy for testing mdconvert (pip install  scripttest) to .travis

commit 5c539cb5862d35882554aa8cad57853db5eda88b
Author: Robert McGibbon <rmcgibbo@gmail.com>
Date:   Sat Jun 29 22:29:20 2013 -0700

    add tests. some failures right now, because it needs to be rebased ontop of PR#106 to work