Sqlite::truncate(): Verify `sqlite_sequence` exists before _execute()

`sqlite_sequence` is a dynamic table that's only available when a table in
the database use an auto increment field.  For some cases, eg: databases that
exclusively use uuid for primary keys, this table won't exist and
truncate() call will fail with:

  Error: SQLSTATE[HY000]: General error: 1 no such table: sqlite_sequence
Reduce variable use/duplicate code.
Added/removed newlines to make the code more readable.
flushMethodCache not working if called before cacheMethod

When calling flushMethodCache it correctly empties self::$methodCache but if cacheMethod is called afterwards self::$methodCache gets populated with data from the Cache.
performance improvements in Model::_clearCache

- don't empty cache twice if pluralized name is identical to underscored
- refactors for fewer function calls
Refactors Model::_clearCache

- don't use mixed keys in $assoc array
- removes unnecessary strtolower on Inflector::underscore result
- return early
Fix issue 4116 and also merge both versions of home.ctp
Merge pull request #1694 from dereuromark/master-home-ctp

Only show the rewrite rule error message if the default CSS is in place.

Fixes #4116
Test case for DboSource::flushMethodCache
Do not assume CONTENT_TYPE is available.

In some server environments notably the CLI server, _SERVER['CONTENT_TYPE'] is not available.
In these cases, fall back to the HTTP_CONTENT_TYPE header.

Refs #GH-1661
Merge pull request 1661 from 'sime/fallback-content-type' to master.
Merge branch 'master' of github.com:cakephp/cakephp
Make String::wrap() unicode aware. Solves #3981.
Merge pull request #1695 from renan/2.4-wordwrap

Make String::wrap() unicode aware. Fixes #3981.
More gracefully handle invalid data in Accept headers.

Some browsers have invalid accept headers, we should ignore the invalid
extension data as assuming it will be a qualifier can result in
incorrect results.

Fixes #4105
Fixing CS errors.
Updated returns in docblocks in File utility
Fixed CS error
Additional grammatical corrections to File utility
Rrue to True, simple typo