tools/configure.sh: Restore support for custom, out-of-tree configurations that was broken in a previous commit.

Documentation/NuttxPortingGuide.html

@@ -1578,7 +1578,7 @@ tools/
   accomplish the same configuration:
 </p>
 <ul><pre>
-  tools/configure.sh [OPTIONS] <i>&lt;board-name&gt;</i>:<i>&lt;config-dir&gt;</i>
+  tools/configure.sh [OPTIONS] <i>&lt;board-name&gt;</i>[:<i>&lt;config-dir&gt;</i>]
 </pre></ul>
 
 <p>
@@ -1587,6 +1587,13 @@ tools/
 <ul><pre>
   tools\configure.bat <i>&lt;board-name&gt;</i>:<i>&lt;config-dir&gt;</i>
 </pre></ul>
+<p>
+  And, to make sure that other platforms are supported, there is also a C program at <code>tools/configure.c</code> that can be compiled to establish the board configuration on all platforms.
+</p>
+<p><blockquote><small>
+  NOTE (2019-08-6):  As of this writing, changes to the boards/ directly have made <code>configure.bat</code> unusable.
+  For the native Windows environment, <code>configure.c</code> is recommended until that batch file can be repaired.
+</small></blockquote></p>
 <p>
   See <code>tools/README.txt</code> for more information about these scripts.
   Or use the -h option with <code>configure.sh></code>
@@ -1594,7 +1601,7 @@ tools/
 <ul><pre>
 $ tools/configure.sh -h
 
-USAGE: tools/configure.sh [-d] [-l|m|c|u|g|n] [-a &lt;app-dir&gt;] &lt;board-name&gt;:&lt;config-name&gt;
+USAGE: tools/configure.sh [-d] [-l|m|c|u|g|n] [-a &lt;app-dir&gt;] &lt;board-name&gt;[:&lt;config-name&gt;]
 
 Where:
   -l selects the Linux (l) host environment.
@@ -1616,7 +1623,7 @@ Where:
   then you should also specify the location of the application directory on the command line like:
 </p>
 <ul><pre>
-  tools/configure.sh -a &lt;app-dir&gt; <i>&lt;board-name&gt;</i>:<i>&lt;config-dir&gt;</i>
+  tools/configure.sh -a &lt;app-dir&gt; <i>&lt;board-name&gt;</i>[:<i>&lt;config-dir&gt;</i>]
 </pre></ul>
 
 <p>