python-3.7.6: Use cached copy of boost download

The distribuition server seems to be broken at the moment:

    + wget https://dl.bintray.com/boostorg/release/1.72.0/source/boost_1_72_0.tar.gz
    --2020-03-28 13:02:47--  https://dl.bintray.com/boostorg/release/1.72.0/source/boost_1_72_0.tar.gz
    Resolving dl.bintray.com... 52.28.187.224, 52.29.129.139
    Connecting to dl.bintray.com|52.28.187.224|:443... connected.
    HTTP request sent, awaiting response... 403 Forbidden
    2020-03-28 13:02:47 ERROR 403: Forbidden.

Use cached copy.

python-3.7.6-0.build.sh

@@ -247,7 +247,9 @@ pip3 install --prefix=$PREFIX multiqc
 	PKGCFLAGS="-O2 -fPIC"
 
 	cd $BUILDDIR
-	test -e boost_${BOOST_VERSION[1]}.tar.gz || wget $BOOST_SRC
+	# 28.03.2020: upstream server currently broken - use cached archive
+	#test -e boost_${BOOST_VERSION[1]}.tar.gz || wget $BOOST_SRC
+	test -e boost_${BOOST_VERSION[1]}.tar.gz || cp /src/mariux/beeroot/downloads/boost_${BOOST_VERSION[1]}.tar.gz .
 	test -d boost-${BOOST_VERSION[0]} || mkdir boost-${BOOST_VERSION[0]} && tar -xf boost_${BOOST_VERSION[1]}.tar.gz -C boost-${BOOST_VERSION[0]} --strip-components=1
 
 	cd boost-${BOOST_VERSION[0]}