json: Store short strings in-place. #3043

Job	Run time
linux deb no dpdk	6m 47s
osx clang --disable-ssl	1m 37s
linux rpm fedora	4m 10s
dpdk gcc	5s
clang-analyze	9m 14s
linux gcc --disable-ssl	3m 21s
linux clang --disable-ssl	2m 45s
linux gcc c99	2m 58s
linux clang c99	2m 27s
linux gcc test	8m 24s
linux clang address,undefined test	16m 17s
linux gcc test --enable-shared	8m 47s
linux clang test --enable-shared	11m 46s
linux gcc check check-dpdk dpdk	18m 18s
linux clang check check-dpdk dpdk	18m 46s
linux gcc test -ljemalloc	8m 45s
linux clang test -ljemalloc	9m 35s
linux gcc --enable-afxdp	2m 20s
linux clang --enable-afxdp	2m 18s
linux gcc dpdk --enable-shared	3m 37s
linux clang dpdk --enable-shared	3m 43s
linux gcc dpdk-shared	2m 55s
linux clang dpdk-shared	2m 40s
linux gcc dpdk-shared --enable-shared	3m 24s
linux clang dpdk-shared --enable-shared	4m 10s
linux gcc m32 --disable-ssl	2m 42s
linux gcc check-ovsdb-cluster	7m 18s
linux gcc check-kernel -100	8m 47s
linux gcc check-kernel 100-	9m 18s
linux clang address,undefined check-kernel -100	12m 47s
linux clang address,undefined check-kernel 100-	12m 11s
linux gcc check-offloads -100	9m 33s
linux gcc check-offloads 100-	7m 47s
linux gcc dpdk check-system-userspace	11m 33s
linux clang address,undefined dpdk check-system-userspace	14m 26s
linux gcc dpdk check-system-tso	13m 16s
linux gcc dpdk check-afxdp	11m 39s
	4h 40m 26s

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