Remove variable declaration from for-loop header and enclose in block

This solves `error: for loop initial declarations are only allowed in C99 mode`
when building on gcc 4.4.7 (Default gcc on CentOS 6.x)

Author: PaulFurtado

oursqlx/_exceptions.c

@@ -618,7 +618,9 @@ enum _oursqlx_exception_type _oursqlx_exc_from_errno(int err) {
 
         default:
             #if MYSQL_VERSION_ID >= 50700
-                for(unsigned int i = 0; i < sizeof(errmsg_section_start)/sizeof(int); ++i) {
+            {
+                unsigned int i;
+                for(i = 0; i < sizeof(errmsg_section_start)/sizeof(int); ++i) {
                     int min = errmsg_section_start[i];
                     int max = errmsg_section_start[i] + errmsg_section_size[i] - 1;
                     if ( err >= min && err <= max ) {
@@ -628,6 +630,7 @@ enum _oursqlx_exception_type _oursqlx_exc_from_errno(int err) {
                 if ( err > CR_MIN_ERROR && err < CR_MAX_ERROR) {
                     return _oursqlx_InterfaceError;
                 }
+            }
             #else
                 if (err >= ER_ERROR_FIRST && err <= ER_ERROR_LAST)
                     return _oursqlx_ProgrammingError;