Add a mecanism similar to the classical errno system for reporting error

but specific to the OBITools framwork

src/obierrno.c

+/*
+ * obierrno.c
+ *
+ *  Created on: 23 mai 2015
+ *      Author: coissac
+ */
+
+
+int obi_errno;
+

src/obierrno.h

+/*
+ * obierrno.h
+ *
+ *  Created on: 23 mai 2015
+ *      Author: coissac
+ */
+
+#ifndef OBIERRNO_H_
+#define OBIERRNO_H_
+
+/**
+ * @brief The declaration of the external variable `obi_errno`.
+ *
+ * `obi_errno` is an equivalent of `errno` for the system level error
+ * but for for error generated by the C layer of the OBITools framework.
+ *
+ * @todo We have to look for defining this variable as thread specific.
+ */
+extern int obi_errno;
+
+/**
+ * @brief set the global `obi_errno` variable with
+ *        the specified `err` code
+ *
+ * This function is defined as a macro to reduce the risk
+ * to increase the problem generating the error by calling
+ * a new function.
+ *
+ * @param err the error code as an integer value
+ *
+ * @since May 2015
+ * @author Eric Coissac (eric.coissac@metabarcoding.org)
+ */
+#define obi_set_errno(err) (obi_errno = (err))
+
+#endif /* OBIERRNO_H_ */