Look for include files in the directory of the including file.

Looking in the diretory dtc is invoked from is not very useful behavior.

As part of the code reorganization to implement this, I removed the
uniquifying of name storage -- it seemed a rather dubious optimization
given likely usage, and some aspects of it would have been mildly awkward
to integrate with the new code.

Signed-off-by: Scott Wood <scottwood@freescale.com>

dtc-parser.y

@@ -309,7 +309,7 @@ label:
 
 void yyerrorf(char const *s, ...)
 {
-	const char *fname = srcpos_filename_for_num(yylloc.filenum);
+	const char *fname = srcpos_file ? srcpos_file->name : "<no-file>";
 	va_list va;
 	va_start(va, s);