TODO: extend login capability note

We cannot remove CAP_SYS_ADMIN, which basically makes removing all other
capabilities useless. Anyhow, still wouldn't hurt checking whether stuff
like CAP_KILL can be dropped from logind.
shared: util.c: unify split and split_quoted
strv: multiple cleanups

- turn strv_merge into strv_extend_strv.
   appending strv b to the end of strv a instead of creating a new strv
- strv_append: remove in favor of strv_extend and strv_push.
- strv_remove: write slightly more elegant
- strv_remove_prefix: remove unused function
- strv_overlap: use strv_contains
- strv_printf: STRV_FOREACH handles NULL correctly
Remove unused variables
shared/install: use char** convention for strvs
journal: Add missing byte order conversions

Convert entry_array.items[0] to host byte order prior to passing it to
chain_cache_put().

[zj: also use le64toh in journal-verify.c]

https://bugs.freedesktop.org/show_bug.cgi?id=73194
Revert "bus: driverd: don't attempt to remove from empty list"

We need to find the real reason for the failure, this just
avoids the symptoms.

This reverts commit 215c7625dd510759290d45d6c46434e4338843ec.
Fix format string mismatch introduced in ab9001a1

src/libsystemd-bus/sd-bus.c: In function 'sd_bus_open_user':
src/libsystemd-bus/sd-bus.c:1104:25: warning: format '%s' expects argument of type 'char *', but argument 3 has type 'long unsigned int' [-Wformat=]
                         asprintf(&b->address, UNIX_USER_BUS_FMT, (unsigned long) getuid());
configure: use POSIX conformant syntax for test

In shells like bash, == and = are equivalent in test contexts. In POSIX
compliant shells, == isn't a valid operator.