Support specifying an OPENSCADPATH environment variable which will ha…

…ve precedence over the hardcoded library paths. First step of issue #125

doc/TODO.txt

@@ -240,6 +240,7 @@ o Collect "all" available OpenSCAD scripts from the internets and run the integr
 MISSING TESTS:
 --------------
 o cmd-line -D variable override
+o OPENSCADPATH env.variable
 o all functions
 o mirror
 o scale

src/parsersettings.cc

@@ -28,7 +28,15 @@ std::string locate_file(const std::string &filename)
 
 void parser_init(const std::string &applicationpath)
 {
-  // FIXME: Append paths from OPENSCADPATH before adding built-in paths
+  // Add path from OPENSCADPATH before adding built-in paths
+	const char *openscadpath = getenv("OPENSCADPATH");
+	if (openscadpath) {
+		add_librarydir(boosty::absolute(fs::path(openscadpath)).string());
+	}
+
+	// FIXME: Support specifying more than one path in OPENSCADPATH
+	// FIXME: Add ~/.openscad/libraries
+	// FIXME: Add ~/Documents/OpenSCAD/libraries on Mac?
 
 	std::string librarydir;
 	fs::path libdir(applicationpath);