library: Change linux version

Added function procps_linux_version() which used to be an
exported integer instead.  Also changed the method of obtaining
the linux version (more correctly the os release) to use a specific
procfs entry. This works for both Linux and FreeBSD.

proc/procps-private.h

@@ -0,0 +1,25 @@
+/*
+ * libprocps - Library to read proc filesystem
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+#ifndef PROCPS_PRIVATE_H
+#define PROCPS_PRIVATE_H
+
+#include <proc/procps.h>
+
+#define PROCPS_EXPORT __attribute__ ((visibility("default")))
+
+#endif