Structural Update (Important)

CORE:
- added new global variable (PRODUCTION_MODE) which is set to either
"dev" or "production", it will alter the amount of detail in error
messages (mainly concerning database interaction)
- error_message() function now has new arguments: error_message("Public
friendly message",$exc=NULL); - it will check what the production mode
is, if it "dev" it will check to see if additional technical information
has been provided ($exc) and will show it if it is present, otherwise it
will simply display the public error message (formatted nicely)

GUIDELINE (re: database dumps)
All database updates should be added to the /dev/database/ folder with
the following naming convention: DAY-MONTH-YEAR_[additional or
clean].sql

e.g. 14/06/2013_additional.sql would mean the dump can be run on an
existing database (and it will only add the missing tables) while
14/06/2013_clean.sql would require a full wipe and import.