ok, it appears we have things working correctly now with the plugin being compiled as C instead of C++

Added flag to slurmdbd.conf TrackSlurmctldDown where if set will mark idle resources as down on a cluster when a slurmctld disconnects or is no longer reachable.

hostlist_deranged_string(): test for overflow
			    
This builds upon the preceding patch, exploiting that hostrange_to_string()
 * returns >= 0 when it has terminated the string with '\0', where  either 
   - n == 0 and it has not written anything or
   - it has written at most n > 0 characters, indicated by returning  n-1 >= 0;
 * returns a negative value to indicate truncation.

Hence hostrange_deranged_string() changed as follows:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 * added 'len < n' as loop condition, to catch the case 'n == 0'
   (also exploiting that NUL-termination is only needed on error);
 * separator now is inserted after all non-first elements
   (to avoid having to undo the last separator);
 * as in preceding patch, replaced 'truncated' variable by a jump label.

hostrange_to_string(): truncation checks

 * turned 'truncated' variable into jump label;
 * loop changes so that the pre-condition is always len < n:
   - if len >= n inside the loop, the a jump to 'truncated' follows,
   - hence loop post-condition is also len < n, so that buf[len] = '\0' works;
 * consistently check ret=snprintf() for "ret < 0 || (len += ret) >= n",
   - if dims > 1, also tests to ensure that len + dims < n,
   - further overflow test after incrementing len for  separator;
 * moved separator test up (inserted when i > hr->lo)
   (to avoid having to undo the last separator).

hostrange_pop()/hostrange_shift(): test for overflow

hostrange_pop():				   
 * retrofitted out_of_memory() test after strdup;
 * tested for negative length/overflow before the while-loop,
   making sure that 'dims' characters also fit in;
 * second snprintf is not tested.

hostrange_shift(): 
 * analogous changes (second snprintf also not tested). 

host_prefix_end(): save variable, factor out common expressions

This saves one variable and factors out the condition common
to the if/else branches.06_hostlist__host_prefix_end.diff

 * return type of strlen is unsigned (size_t), hence strlen(hostname) >= 0;
 * both while-loops require idx >= 0, hence -1 is returned
   if strlen(hostname) == 0.