Error check macros

For error checking in the TBCI library, the macros BCHK and BCHKNR are used.

Their behaviour depends on the setting of some preprocessor symbols:

ERRCHECK: If not defined, the BCHK/BCHKNR will be ignored If defined, the error checking will be enabled. By default, a message is printed to stderr (cerr) with some explanation what went wrong. BCHK then returns the return value rtval specified as last argument, BCHKNR just carries on.

ABORT_ON_ERR: If defined, after priting a message, abort () will be called on every error detected. (No difference between BCHK and BCHKNR ...). Useful if you use a debugger and want to ger a nice backtrace.

EXCEPT: Use exception handling. An exception of type exc is thrown which can be caught by your app. All TBCI exceptions are derived from TBCI::NumErr.

Parameters:

	cond	- condition to check. Should evaluate to true, if there is an error
	exc	- exception to be thrown
	txt	- text to be printed (or stored in the TBCI::NumErr::errtext member
	ind	- index to print (or store in TBCI::NumErr::index) in case of out-of-bound errors
	rtval	- value to return to caller