Open-code isprint(c) and isspace(c)

Open-code isprint(c) and isspace(c)

We don't call setlocale, thus we always use C locale.
But libc supports various other locales, and therefore
its ctype interface is general and at times inefficient.
For example, in glibc these macros result in function call,
whereas for e.g. isprint(c) just c >= ' ' && c <= 0x7e
suffices.

By open-coding ctype checks (we have only 4 of them)
we avoid function calls, we get smaller code:

   text	   data	    bss	    dec	    hex	filename
 245127	    680	   5708	 251515	  3d67b	strace_old
 245019	    676	   5708	 251403	  3d60b	strace

and we don't link in ctype tables (beneficial for static builds).

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>