[Axis2] Clean up, tidy up and group error codes

[Samisa Abeysinghe <sa...@gmail.com>]

Hi All,
    Inspired by a point made by Nabeel, we have to organize the current 
error code set.
    Given that we have to expose some of the error codes to the user to 
be used at service skeletons and client stubs, we need to have a clear 
way of making the error codes distingushable from each other and also 
help with locating the error codes with ease.
    Some of the error codes we are using now are quite ambiguous. e.g. 
AXIS2_ERROR_NULL_BODY. I am not sure if this is a SOAP body related 
error or HTTP POST request body related error :(

    So lets group the error codes by module and come up with a naming 
convention:
    AXIS2_ERROR_[module name in all capitals]_ERROR_CODE_NAME
    for common errors like OUT_OF_MEMORY, we may use SYSTEM in place of  
[module name in all capitals].

     We need the help from all the folks who put the errors in error.h 
to fix this situation as we have around 200 error codes now. So please 
look after the error codes you have put into the header. Lets use a 
comment to indicate the error groups. e.g.
    /***** OM related error codes *****/
    /** Document root is NULL, when it is not supposed to be NULL */
    AXIS2_ERROR_OM_INVALID_DOCUMENT_STATE_ROOT_NULL.
   
    /***** SOAP related error codes ****/
    /** only one SOAP fault allowed in SOAP body */
    AXIS2_ERROR_SOAP_ONLY_ONE_SOAP_FAULT_ALLOWED_IN_BODY,

NOTE: grouping the current error codes and changing their order would 
not have an impact on error message setting logic. Please see error.c 
for details.

Thanks,
Samisa...