fix(grcc): bounds checking for coupling, nodes, etc

[jodavies]

Cases where we check an array index against, for eg, GRCC_MAXNCPLG should use > and not >=. Cases where we are inserting a new vector entry must remain >= since we about to increment, and then index.

Also increase the default GRCC_MAXNCPLG and GRCC_MAXLEGS to 15.

---

Not all cases should be > rather than >=. For eg, here

form/sources/grcc.cc

Lines 2135 to 2137 in b7753d5

	if (nParticles >= GRCC_MAXMPARTICLES) {
	erEnd("particle table overflow (GRCC_MAXMPARTICLES)");
	}

we check for nParticles >= GRCC_MAXMPARTICLES because below we increment before using nParticles as an index:

form/sources/grcc.cc

Lines 2168 to 2169 in b7753d5

	pid = nParticles++;
	particles[pid] = new Particle(this, pid, pinp);

Fixes #887

[coveralls]

coverage: 65.748%. remained the same — jodavies:issue-887 into form-dev:master