GSV sentence with 0 to 4 satellites, plus gcc -Wfloat-equal

This patch set fixes parsing of shorter GSV sentences that list less than 4 satellites (without commas).

Along the way, fixed warnings

gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-3)

on CentOS 6.5 x86_64

using the following CFLAGS (locally inserted into Makefile)

CFLAGS = -g -Wall -Wextra -Wformat=2 -funsigned-char -fstrict-aliasing
 -Wstrict-aliasing -Wfloat-equal -Wundef -Wuninitialized -Wpointer-arith
 -Wbad-function-cast -Wcast-qual -Wcast-align -Wwrite-strings -Waddress
 -Waggregate-return -Wstrict-prototypes -Wold-style-declaration
 -Wold-style-definition -Wmissing-parameter-type -Wmissing-prototypes
 -Wmissing-declarations -Wmissing-field-initializers -Wmissing-noreturn
 -Wmissing-format-attribute -Wpacked -Wredundant-decls -Wnested-externs
 -Wshadow -Wsign-compare -Wlogical-op -std=c99

and this make command:

make clean ; make example tests