Prevent memory leaks during error/early exist

[dschlaep]

Currently, we call LogError() when the code encounters a problem and, if the problem is an error, then we exit early (i.e., crash for SOILWAT2 -- in case of rSOILWAT2, we call the R_int.h function error() instead).

However, we are not de-allocating dynamically allocated memory. For a single SOILWAT2 run, the program crashes and the OS may/should clean it up. However, in rSOILWAT2, we return to the calling function prematurely, and this causes a memory leak. Similarly, if we will convert SOILWAT2 in the future to run with multiple threads, then a prematurely returning thread will cause a memory leak.

Suggested solution: after we identify the problem but before we call exit() (or similar), we need to de-allocate dynamically allocated memory.