Updated all cases of exit() to return a valid code

Specific codes are as follows, but can easily be changed if a different order/breakdown makes more sense:

- 0: Success; everything executed as planned
- 1: Configuration Error; something is wrong with/in the configuration file(s)
- 2: Class Not Found; what it says
- 3: Driver Method Unsupported; the method you're trying to use on a Driver doesn't exist
- 4: File Not Found; 404 error
- 5: Database Error; something is broken in the database somewhere
- 6: Invalid Input; the user attempted to submit a request with invlaid characters in 1+ key names
7 through 26 are reserved for future use
- 27: Generic Error; generated by show_error() when the status code is >= 100
28 through 127 are errors generated by user applications, normally by using show_error() with a status code below 100
128 through 254 should not be used by applications, as they are reserved by system-level functions
- 255: PHP Fatal Error; automatically generated by PHP for fatal errors, and therefore not allowed for our use

Status codes below 100 are shifted up by 28 to place them in the user error range.  It may make more sense to have these codes
left alone and instead shift the CI errors into the 101 through 127 space, but that's not what I opted for here.

It would probably also be a good idea to replace the hard-coded numbers with constants or some such, but I was in a bit of a
hurry when I made these changes, so I didn't look around for the best place to do this.  With proper guidance, I could
easily amend this commit with another that uses such constant values.

Signed-off-by: Daniel Hunsaker <danhunsaker@gmail.com>
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
Fix newline standardization.

Signed-off-by: Eric Roberts <eric@cryode.com>
Merge pull request #2198 from cryode/bug/input-newline

Fix newline standardization.
Remove unnecessary defined('ENVIRONMENT') checks

As suggested in issue #2134 & PR #2149
Merge branch 'develop' of github.com:EllisLab/CodeIgniter into develop
Add ENVIRONMENT constant to unit tests
Multiple pagination bug fixes & optimizations.

Signed-off-by: Eric Roberts <eric@cryode.com>
Fix auto_link() for the Nth time

 - anchor() is for local links and breaks ones that don't have a protocol prefix
 - Allow :// links (no actual protocol specified)
 - Further simplified the URL regular expression
Upload library, clean_file_name function: Fix xss bug.

For example: If you clear this string "%%3f3f" according to the $bad array will fail. The result will be "%3f"
Because str_replace() replaces left to right.

Signed-off-by: xeptor <servetozkan@live.com>
Remove str_replace in return
Merge pull request #2201 from xeptor/develop

Upload library, clean_file_name function: Fix xss bug.
Libraries' filenames must be named in a ucfirst-like manner