Removed slash from URI helper doc

In my current projects I don't see '/controller/method' but 'controller/method' when calling uri_string().
Merge pull request #2186 from 12k/patch-1

Removed slash from URI helper doc
Move db_select() call from CI_DB_driver::initialize() to db_connect()
so that it's only called by drivers that need it ('mysql', 'mssql').

As proposed in issue #2187.
Fix issue #2191.

Signed-off-by: Edwin Aw <tkaw220@gmail.com>
Merge pull request #2192 from tkaw220/develop

Fix issue #2191.
Fix a code comment in Image_lib

constant FILE_WRITE_MODE contains octal 0666
Merge pull request #2194 from vlakoff/develop

Fix a code comment in Image_lib
Add webm mime type

http://www.webmproject.org/about/faq/
Merge pull request #2195 from rebornishard/patch-1

Add webm mime type
Fixing issue with comma
Merge pull request #2197 from dontforget/patch-1

Fixing issue with comma