(2143) Get PouchDB's scripts to run properly on Windows

bin/build-plugin.sh - The resolve library in browerify acts differently on
Linux and Windows when
resolving ./lib/deps/migrate. But getting rid of the path and just using
the package name migrate (since this is a rename) seems to work
in both places. Also got rid of the accidental duplication of the migrate
line.

package.json - For calls to sh scripts change the call from being a path
 starting with './bin/' to start with 'sh bin/' and change calls to js
 files to change from './bin/' to 'node ./bin/'. Also had to set
 run-test.sh to use 'bash' and not 'sh' because it's a bash script.

test.attachments.js - Added the hashes for the attachments generated
by CouchDB on Windows. For some reason they are different than those
on Linux. We really should remove these hashes all together, please
see #3156
(#3146) - Adding pull replication performance tests

perf.basics.js - Add three tests. One does a pull replication against skimdb and is
disabled by default. The second and third tests test pull replication against a local
DB over the network. The difference between the tests is that one uses first generation
documents and the other uses second generation documents.

test/performance/utils.js - Fixed so that if iterations == 0 a test won't run and
also added a per test tear down functionality.

common-utils.js - Created this file to hold some, well, common utilities.

replication-test.js - Contains the pull replication test framework.

A huge thanks to daleharvey for taking the time to rework the content
in replication-test.js so it would be acceptable to the group!
(#2907) - Updating 'Common Errors' page

...with 'No valid adapter found' error, and 'Unknown
(Chrome/Opera)' error explanations.
(#3160) - Remove redundant jshint dir
(#3136) - fix changes() when earlier winning seq

In the previous version of the changes() algorithm,
we were assuming that the winning seq was later than
all non-winning seqs, which isn't necessarily the case
when you've got conflicts. This fixes that.
(#3169) - edit guide to changes

Now that I understand `last_seq` better, I understand
that it is not a footgun.