DEBUG POPULATE two args form implemented.

The old DEBUG POPULATE form for automatic creation of test keys is:

    DEBUG POPULATE <count>

Now an additional form is available:

    DEBUG POPULATE <count> <prefix>

When prefix is not specified, it defaults to "key", so the keys are
named incrementally from key:0 to key:<count-1>. Otherwise the specified
prefix is used instead of "key".

The command is useful in order to populate different Redis instances
with key names guaranteed to don't collide. There are other debugging
uses, for example it is possible to add additional N keys using a count
of N and a random prefix at every call.
redis-trib should not abort easily on connection issues.
Improve disable save comment in redis.conf

Closes #1897
Remove surplus double quotes

Closes #1877
Update linenoise accessory files

The core linenoise code was being backported, but not
the README or example.  It's less confusing for users
if everything matches across directories.

Fix inspired by @thrig

Closes #1872
Fix many small typos

Closes #1871
Fix incorrect comments

error != success; and 0 != number of bytes written

Closes #1806
Fix typo in redis.conf

Closes #1713
Fix typo

Closes #1682
Fix typo

Closes #1544
Fix typo: ad -> and

Closes #1537
Fix typos

Closes #1513
Grammar and typo fixes in redis.conf

Closes #1441
Fix typo in redis.h

Closes #1386
Fix on-place -> in-place

Closes #1373
Fix hash table size in comment for dictScan

Closes #1351
Clean up text throughout project

  - Remove trailing newlines from redis.conf
  - Fix comment misspelling
  - Clarifies zipEncodeLength usage and a C API mention (#1243, #1242)
  - Fix cluster typos (inspired by @papanikge #1507)
  - Fix rewite -> rewrite in a few places (inspired by #682)

Closes #1243, #1242, #1507
Spell software correctly
Fix spelling in some test cases
Remove trailing spaces from tests