Adding CT_NG_COMPONENTS prefetching, using sha1 checksums

crosstool-ng config files are generated by:
./ct-ng menuconfig
at:
<BUILDDIR>/crosstool-ng/crosstool-ng-1.19.0

gpg keys are verified using keys.gnupg.net keyserver

CT_NG_COMPONENTS are cached at:
https://dev.cumulusnetworks.com/~curt/mirror/onie/crosstool-NG/

Downloaded files checksums (non sha1) verification origin:
strace-4.6.tar.xz
  http://sourceforge.net/projects/strace/files/strace/4.6/strace-4.6.tar.xz.asc
ppl: Parma Polyhedra Library (Release 0.11.2)
  ftp://ftp.cs.unipr.it/pub/ppl/releases/0.11.2/ppl-0.11.2.tar.lzma.sign
upstream/mpfr-2.4.2.tar.bz2.sha1
  https://ftp.gnu.org/gnu/mpfr/mpfr-2.4.2.tar.bz2.sig
upstream/mpc-1.0.1.tar.gz.sha1
  https://ftp.gnu.org/gnu/mpc/mpc-1.0.1.tar.gz.sig
upstream/make-3.81.tar.bz2.sha1
  https://ftp.gnu.org/gnu/make/make-3.81.tar.bz2.sig
upstream/m4-1.4.13.tar.xz.sha1
  https://ftp.gnu.org/gnu/m4/m4-1.4.13.tar.xz.sig
upstream/ltrace_0.5.3.orig.tar.gz.sha1
  http://ftp.de.debian.org/debian/pool/main/l/ltrace/ltrace_0.5.3-2.1.dsc
upstream/libtool-2.2.6b.tar.lzma.sha1
  https://ftp.gnu.org/gnu/libtool/libtool-2.2.6b.tar.lzma.sig
upstream/libelf-0.8.13.tar.gz.sha1
  http://www.mr511.de/software/  has no md5sums.
  Md5sum verified with:
    http://lists.freebsd.org/pipermail/freebsd-ports-bugs/2009-November/176537.html
    https://dev.openwrt.org/browser/packages/libs/libelf/Makefile?rev=20985
  We are downloading from:
    http://dev.cumulusnetworks.com/~curt/mirror/onie/crosstool-NG/libelf/libelf-0.8.13.tar.gz
  http://packages.ubuntu.com/trusty/libelfg0 has a different checksum
upstream/gmp-4.3.2.tar.bz2.sha1
  https://ftp.gnu.org/gnu/gmp/gmp-4.3.2.tar.bz2.sig
upstream/gdb-7.4.1.tar.bz2.sha1
  https://ftp.gnu.org/gnu/gdb/gdb-7.4.1.tar.bz2.sig
upstream/gcc-4.7.3.tar.bz2.sha1
  https://ftp.gnu.org/gnu/gcc/gcc-4.7.3/gcc-4.7.3.tar.bz2.sig
upstream/duma_2_5_15.tar.gz.sha1
  http://sourceforge.net/projects/duma/files/duma/2.5.15/
  sha1: f1f90620c5eff4e76316594fa3e7e5a6833b8d0d
upstream/cloog-ppl-0.15.10.tar.gz.sha1
  could not find former versions in: http://www.cloog.org/
  md5sum verified by:
    https://dev.openwrt.org/browser/trunk/tools/cloog/Makefile?rev=29293
    https://mailman.archlinux.org/pipermail/arch-commits/2010-December/113420.html
  We are downloading from:
    http://dev.cumulusnetworks.com/~curt/mirror/onie/crosstool-NG/cloog-ppl-0.15.10.tar.gz
upstream/binutils-2.22.tar.bz2.sha1
  https://ftp.gnu.org/gnu/binutils/binutils-2.22.tar.bz2.sig
upstream/automake-1.11.1.tar.bz2.sha1
  https://ftp.gnu.org/gnu/automake/automake-1.11.1.tar.bz2.sig
upstream/autoconf-2.65.tar.xz.sha1
  https://ftp.gnu.org/gnu/autoconf/autoconf-2.65.tar.xz.sig

Tests:

1. Verify git status is clean with no untracked files
2. make BUILDDIR=<new x86 build folder> all -j8
3. make BUILDDIR=<new ppc build folder> all MACHINE=fsl_p2020rdbpca -j8

Signed-off-by: Doron Tsur <doront@mellanox.com>
Signed-off-by: Curt Brune <curt@cumulusnetworks.com>