Rename openlibm.h to openlibm_math.h.

This is a bit more consistent with the naming of the other header files
(openlibm_complex.h and openlibm_fenv.h). Re-add an openlibm.h header
that includes all of the public headers as a shorthand.

Fix up all of the source files to include <openlibm_math.h> instead of
<openlibm.h>. While there, fix ordering of the includes.

Author: EdSchouten

bsdsrc/b_exp.c

@@ -31,6 +31,7 @@
 #include "cdefs-compat.h"
 //__FBSDID("$FreeBSD: src/lib/msun/bsdsrc/b_exp.c,v 1.9 2011/10/16 05:37:20 das Exp $");
 
+#include <openlibm_math.h>
 
 /* EXP(X)
  * RETURN THE EXPONENTIAL OF X

bsdsrc/b_log.c

@@ -31,8 +31,7 @@
 #include "cdefs-compat.h"
 //__FBSDID("$FreeBSD: src/lib/msun/bsdsrc/b_log.c,v 1.9 2008/02/22 02:26:51 das Exp $");
 
-#include <openlibm.h>
-#include <errno.h>
+#include <openlibm_math.h>
 
 #include "mathimpl.h"
 

bsdsrc/b_tgamma.c

@@ -38,7 +38,8 @@
  * acknowledged.
  */
 
-#include <openlibm.h>
+#include <openlibm_math.h>
+
 #include "mathimpl.h"
 
 /* METHOD:

bsdsrc/mathimpl.h

@@ -34,8 +34,6 @@
 #define	_MATHIMPL_H_
 
 #include "cdefs-compat.h"
-#include <openlibm.h>
-
 #include "math_private.h"
 
 /*