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>
Multiple pagination bug fixes & optimizations.

Signed-off-by: Eric Roberts <eric@cryode.com>
Remove spaces from concats.

Signed-off-by: Eric Roberts <eric@cryode.com>
Move $get assignment to if/else.

Signed-off-by: Eric Roberts <eric@cryode.com>
Replace is_numeric() with ctype_digit()

Signed-off-by: Eric Roberts <eric@cryode.com>
Added Form Validation rule for alphanum + spaces.

Signed-off-by: Sajan Parikh <sajan@noppix.com>
Fixed documentation.

Signed-off-by: Sajan Parikh <sajan@noppix.com>
Added error message in lang file.

Signed-off-by: Sajan Parikh <sajan@noppix.com>
Cleaned up for pull request.

Signed-off-by: Sajan Parikh <sajan@noppix.com>
Add entry in user guide changelog.

Signed-off-by: Sajan Parikh <sajan@noppix.com>
Merge pull request #2220 from sajanNOPPIX/develop

New Form Validation Rule: alpha_numeric_spaces
Added 'application/x-zip' mimetype for docx
Merge pull request #2227 from Lasha/patch-1

Added 'application/x-zip' mimetype for docx
Allow non-string values to be used as captcha words (issue #2215)
[ci skip] Add a missing space
Merge pull request #2199 from cryode/feature/pagination

Multiple pagination bug fixes & optimizations.
[ci skip] Remove unnecessary string casts in Pagination
Fix issue #2230
Added small feature to profiler: total execution time count

adds additional information to profiler like:
DATABASE:  test   QUERIES: 3 (0.0016s)  (Hide)
Update system/core/Log.php

Updated Log.php so that a developer can extend it and change the log file extension.

It makes sense to default to .php when logs are in the public web folder.  It would be nice if a developer moves the log file path we have the option to use a standard extension like .log