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Use strncmp() combined with a strlen() will give better performance
than a strstr in worst case. Especially when the match prefix is a
constant and not a variable.

While we are at it, replace the match() function in linux/Battery.c,
which uses a naive algorithm, with a macro that does better job by
utilizing Strings_startWith().

    $ gcc --version | head -n 1
    gcc (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4
    $ uname -m
    x86_64
    $ size htop.old htop.new
       text   data    bss    dec    hex filename
     137929  15112   3776 156817  26491 htop.old
     137784  15104   3776 156664  263f8 htop.new

Signed-off-by: Kang-Che Sung <explorer09 @ gmail.com>