Minor build improvements.

The build_linux.sh scripts stops when encountering an error
and reports what it is doing.

Directories constructed temporarily during the build
and files commonly constructed by the build
ignored by git, as we do not want to version those.

/usr/bin has become the official dwelling place of bash.

.gitignore

@@ -0,0 +1,13 @@
+/build_linux/
+/build_osx/
+/codec2/
+/hamlib/
+/hamlib-code/
+/LPCNet/
+/macdylibbundler/
+
+a.out
+*.o
+*.make
+*.log
+*.marks

build_linux.sh

@@ -1,9 +1,12 @@
-#!/bin/bash
+#!/usr/bin/bash
 # build_ubuntu.sh
 #
 # Build script for Ubuntu and Fedora Linux, git pulls codec2 and
 # lpcnet repos so they are available for parallel development.
 
+# Echo what you are doing, and fail if any of the steps fail:
+set -x -e
+
 export FREEDVGUIDIR=${PWD}
 export CODEC2DIR=$FREEDVGUIDIR/codec2
 export LPCNETDIR=$FREEDVGUIDIR/LPCNet