the same vector as long as the new max size is the same as the old one.
git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@5471 c06c8d41-db1a-0410-9941-cceddc491573
CRQZPF2BLLIDXCUOBLYDBDA5TC26EE7R7DTO76SMCQWDINVEW5SAC
K2GMFKXUWN5R3KCW6OYVXHN47MIQZKEEIOSAU6LFFKBNKF6JBVWAC
ASSERT(max_size == VEC_MAX_SIZE);
ASSERT(max_size == VEC_MAX_SIZE || max_size == _size);