devd: Avoid the creation of a temporary object...

...by using the prefix operator for non-primitive types.

Obtained From: FreeBSD (r243931)
devd: Prefer the use of initializer lists to ctor assignment
devd: Use volatile sig_atomic_t...

...for the flag set by a signal handler. Remove call to _exit() from signal
handler, which also sets a stop flag.

Obtained From: FreeBSD
devd: Use 'const' where possible
devd: Use string::empty() instead of string::length() == 0

Obtained From: FreeBSD
devd: Use simpler dst += *x instead of str.append(x, 1)

Also fix typo in comment

Obtained From: FreeBSD
devd: Prefer using the C++ version of the standard headers

These place the names within the std namespace (and possibly within the
global namespace).

The main advantage is that the C++ versions can provide optimized versions
or simplified interfaces.

Obtained From: FreeBSD (r250186)
bsd-family-tree: Sync with FreeBSD (adds OpenBSD 5.3 & DragonFly 3.4.1).