src/tool: allow timeouts to accept decimal values

Implement wrappers around strtod to convert the user argument to a
double with sane error checking. Use this to allow --max-time and
--connect-timeout to accept decimal values instead of strictly integers.

The manpage is updated to make mention of this feature and,
additionally, forewarn that the actual timeout of the operation can
vary in its precision (particularly as the value increases in its
decimal precision).

src/tool_paramhlp.c

@@ -187,6 +187,48 @@ ParameterError str2unum(long *val, const char *str)
   return PARAM_OK;
 }
 
+/*
+ * Parse the string and write the double in the given address. Return PARAM_OK
+ * on success, otherwise a parameter specific error enum.
+ *
+ * Since this function gets called with the 'nextarg' pointer from within the
+ * getparameter a lot, we must check it for NULL before accessing the str
+ * data.
+ */
+
+ParameterError str2double(double *val, const char *str)
+{
+  if(str) {
+    char *endptr;
+    double num = strtod(str, &endptr);
+    if((endptr != str) && (endptr == str + strlen(str))) {
+      *val = num;
+      return PARAM_OK;  /* Ok */
+    }
+  }
+  return PARAM_BAD_NUMERIC; /* badness */
+}
+
+/*
+ * Parse the string and write the double in the given address. Return PARAM_OK
+ * on success, otherwise a parameter error enum. ONLY ACCEPTS POSITIVE NUMBERS!
+ *
+ * Since this function gets called with the 'nextarg' pointer from within the
+ * getparameter a lot, we must check it for NULL before accessing the str
+ * data.
+ */
+
+ParameterError str2udouble(double *val, const char *str)
+{
+  ParameterError result = str2double(val, str);
+  if(result != PARAM_OK)
+    return result;
+  if(*val < 0)
+    return PARAM_NEGATIVE_NUMERIC;
+
+  return PARAM_OK;
+}
+
 /*
  * Parse the string and modify the long in the given address. Return
  * non-zero on failure, zero on success.