error handling

[martynpclark]

The error handling is somewhat ad-hoc, with error codes largely selected at random.

The convention is as follows:
0 = OK
positive = fatal error
negative = warning (or recoverable error)

We should really use named variables in globalData.f90, i.e.,

integer(i4b),parameter,public :: ok=0
integer(i4b),parameter,public :: recoverableError=-1
integer(i4b),parameter,public :: fatalError=1

Then the error checking can (in most cases) be

if(err/=ok)then
 message=trim(message)//trim(cmessage)
 return
endif

or (in special cases

if(err==recoverableError) [doSomething]

Note that this will change MANY lines of code, so should be included as a separate branch.

[bartnijssen]

Also see issue #14