Since we're already installing man pages conditionally
(only install a man page when the corresponding program is enabled),
it makes more sense to install them by default,
instead of having to install separately with `make install-man`.
Do not force 64-bit `time_t` on 32-bit platforms, since libfuse
does not do so. Linking shared objects with incompatible types
breaks ABI, resulting in undefined behavior.
Instead, add run-time checks to make sure that timestamps do not
overflow. If they do, set to `INT32_MAX`.
Also tidy up build scripts, tests, and the installation guide.