Add extra_float_digits connection option defaulted to 3

Add a connection option for setting extra_float_digits and set its
default value to 3. This allows for more accurate representation of
large floating point values.

The option is sent in the connection startup packet so as not to incur
an extra round trip. This will not work with older database that do
not support setting the extra_float_digits connection parameter in the
startup packet (PostgreSQL versions <=8.4).

Closes brianc#730

WARNING: This is a breaking change and will prevent connecting to older
         (<=8.4) databases unless extra_float_digits is set to 0.

Author: sehrope

lib/client.js

@@ -208,6 +208,11 @@ Client.prototype.getStartupConf = function() {
     data.application_name = appName;
   }
 
+  var extraFloatDigits = params.extra_float_digits;
+  if( extraFloatDigits ) {
+    data.extra_float_digits = String(extraFloatDigits);
+  }
+
   return data;
 };
 

lib/connection-parameters.js

@@ -48,6 +48,7 @@ var ConnectionParameters = function(config) {
 
   this.application_name = val('application_name', config, 'PGAPPNAME');
   this.fallback_application_name = val('fallback_application_name', config, false);
+  this.extra_float_digits = val('extra_float_digits', config, false);
 };
 
 var add = function(params, config, paramName) {

lib/defaults.js

@@ -41,7 +41,12 @@ var defaults = module.exports = {
   ssl: false,
 
   application_name : undefined,
-  fallback_application_name: undefined
+  fallback_application_name: undefined,
+
+  //number of digits displayed for floating-point values
+  //set to 0 to suppress sending it as part of the startup packet
+  //must be explicitly set to 0 to for driver to work with PG <= 8.4
+  extra_float_digits: 3
 };
 
 //parse int8 so you can get your count values as actual numbers