Replace stoul with ToIntegral in dbwrapper

[maflcko]

The string is created with %llu. See:

bitcoin/src/leveldb/db/db_impl.cc

Lines 1436 to 1437 in 7fcf53f

	snprintf(buf, sizeof(buf), "%llu",
	static_cast<unsigned long long>(total_usage));

So it seems odd to silently accept when parsing: whitespace, a sign character, trailing chars, overflow, ....

Fix that by using the stricter ToIntegral.

[practicalswift]

Concept ACK

Very happy to see the KNOWN_VIOLATIONS list in test/lint/lint-locale-dependence.sh shrink. Only a few violations left to tackle! :)

[laanwj]

Code review ACK fa165e9

[theStack]

Code-review ACK fa165e9

[practicalswift]

cr ACK fa165e9