git-svn: fix localtime=true on non-glibc environments

git-svn: fix localtime=true on non-glibc environments

git svn uses POSIX::strftime('%s', $sec, $min, ...) to make unix epoch time.
But lowercase %s formatting character is a GNU extention. This causes problem
in git svn fetch --localtime on non-glibc systems, such as msys or cygwin.
Using Time::Local::timelocal($sec, $min, ...) fixes it.

Signed-off-by: Ryuichi Kokubo <ryu1kkb@gmail.com>
Signed-off-by: Eric Wong <normalperson@yhbt.net>
Notes:
    lowercase %s format character in strftime is a GNU extension and not widely supported.
    POSIX::strftime affected by underlying crt's strftime because POSIX::strftime just calls crt's one.
    Time::Local is good function to replace POSIX::strftime because it's a perl core module function.

    Document about Time::Local.
     http://perldoc.perl.org/Time/Local.html

    These are specifications of strftime.

    The GNU C Library Reference Manual.
     http://www.gnu.org/software/libc/manual/html_node/Formatting-Calendar-Time.html

    perl POSIX module's strftime document. It does not have '%s'.
     http://perldoc.perl.org/POSIX.html

    strftime document of Microsort Windows C Run-Time library.
     https://msdn.microsoft.com/en-us/library/fe06s4ak.aspx

    The Open Group's old specification does not have '%s' too.
     http://pubs.opengroup.org/onlinepubs/007908799/xsh/strftime.html

    On my environment, following problems happened.
    - msys   : git svn fetch does not progress at all with perl.exe consuming CPU.
    - cygwin : git svn fetch progresses but time stamp information is dropped.
       Every commits have unix epoch timestamp.

    I would like to thank git developer and contibutors.
    git helps me so much everyday.
    Thank you.

Signed-off-by: Junio C Hamano <gitster@pobox.com>