Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

Fix bad error messages from dpv(3)

Before = dpv: <__func__>: posix_spawnp(3): No such file or directory
After = dpv: <path/cmd>: No such file or directory

Most notably, show the 2nd argument being passed to posix_spawnp(3)
so we know what path/cmd failed.

Also, we don't need to have "posix_spawnp(3)" in the error message
nor the function because that can [a] change and [b] traversed using
a debugger if necessary.

Fix fatal warn when compiling under GCC 5.2.0

GCC 5.2.0 generates the following [fatal] warning:
dialog_util.c:270:23: error:
zero-length gnu_printf format string [-Werror=format-zero-length]
sprintf(dargv[n++], "");

Fix malloc argument while here, removing sprintf.

Reported by: Ruslan Bukin <ruslan.bukin at cl cam ac uk>

Fix a crash if `-D' is used without `-t title'

dialog(3)'s dlg_reallocate_gauge(), used both by dialog(3)'s dialog_gauge()
and dialog(1)'s `--gauge', will segmentation fault in strlen(3) if no title
is set for the widget. Reproducible with `dialog --gauge hi 6 20' (adding
`--title ""' is enough to prevent segmentation fault).

MFC after: 3 days
X-MFC-to: stable/10

Make libdpv [dpv(3)] WARNS=6 clean for clang on -CURRENT.
NB: aka unbreak the build

Reviewed by: shurd
MFC after: 21 days
X-MFC-to: stable/10 stable/9
X-MFC-with: 274116 274120

Add new libraries/utilities for data throughput visualization.
dpv(3): dialog progress view library
dpv(1): stream data from stdin or multiple paths with dialog progress view
figpar(3): configuration file parsing library

Reviews: D714
Reviewed by: jelischer, shurd
Discussed at: MeetBSD California 2014 Vendor/Dev Summit
Discussed on: -current
MFC after: 21 days
X-MFC-to: stable/10 stable/9