macosx: Make build more portable and general

This broadens the OS X build support to include old and current OS
X/Xcode, and Homebrew/MacPorts.

Support pkgbuild/productbuild + metadata from Mosh-1.2.4-3 package
Search for protobufs in /{usr,opt}/local
Make build select pkgbuild if available, PackageMaker if not
Make PackageBuilder build work on OS X 10.5, XCode 3.1, Macports
Do version substitution
Use generic names for c/c++/cpp
Make build script arch-indepdendent
Changes install dir from /usr to /usr/local

Closes #633.

Signed-off-by: John Hood <cgull@glup.org>

macosx/Distribution.in

@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="utf-8" standalone="no"?>
+<installer-script minSpecVersion="1.000000" authoringTool="com.apple.PackageMaker" authoringToolVersion="3.0.6" authoringToolBuild="201">
+    <title>@PACKAGE_VERSION@</title>
+    <options customize="never" allow-external-scripts="no"/>
+    <domains enable_anywhere="true"/>
+    <readme file="ReadMe"/>
+    <license file="License"/>
+    <choices-outline>
+        <line choice="choice0"/>
+    </choices-outline>
+    <choice id="choice0" title="Default" customLocation="/usr">
+        <pkg-ref id="edu.mit.mosh.mosh.pkg"/>
+    </choice>
+    <pkg-ref id="edu.mit.mosh.mosh.pkg" installKBytes="2204" version="@PACKAGE_VERSION@" auth="Root">#edu.mit.mosh.mosh.pkg</pkg-ref>
+</installer-script>