golang: Fix version numbering mistake

Apt considers 1.5.1.rel to be a lower version than 1.5.rel so the
golang 1.5 package was never updated to 1.5.1.

Fix that by introducing an epoch number (1) and prefix it to 1.5.1,
so that the resulting version number 1:1.5.1 is considered higher.

Thanks to Kristof Kovacs for reporting.

packages/golang/build.sh

@@ -2,18 +2,21 @@ TERMUX_PKG_HOMEPAGE=https://golang.org/
 TERMUX_PKG_DESCRIPTION="Go programming language compiler"
 _MAJOR_VERSION=1.5.1
 # Need to be considered a higher version than "1.5rc1":
-TERMUX_PKG_VERSION=${_MAJOR_VERSION}.rel
+TERMUX_PKG_VERSION=1:$_MAJOR_VERSION
 TERMUX_PKG_SRCURL=https://storage.googleapis.com/golang/go${_MAJOR_VERSION}.src.tar.gz
 TERMUX_PKG_FOLDERNAME=go
 TERMUX_PKG_KEEP_STATIC_LIBRARIES=true
 
-TERMUX_HOST_GOLANG_DIR=$TERMUX_PKG_CACHEDIR/go-host-$TERMUX_PKG_VERSION
+TERMUX_HOST_GOLANG_DIR=$TERMUX_PKG_CACHEDIR/go-host-$_MAJOR_VERSION
 
 termux_step_post_extract_package () {
 	if [ ! -d $TERMUX_HOST_GOLANG_DIR ]; then
 		cd $TERMUX_PKG_CACHEDIR
-		curl -o go-host.tar.gz https://storage.googleapis.com/golang/go${_MAJOR_VERSION}.linux-amd64.tar.gz
-		tar xf go-host.tar.gz
+		GOHOST_TARFILE=go-host-${_MAJOR_VERSION}.tar.gz
+		if [ ! -f $GOHOST_TARFILE ]; then
+			curl -o $GOHOST_TARFILE https://storage.googleapis.com/golang/go${_MAJOR_VERSION}.linux-amd64.tar.gz
+		fi
+		tar xf $GOHOST_TARFILE
 		mv go $TERMUX_HOST_GOLANG_DIR
 	fi
 }