MDL-17868 detection of incorrect hadnling of floats in version numbers - this should prevent dataloss in case it does not work as expected

admin/index.php

@@ -61,6 +61,10 @@
         error("The PHP server variable 'file_uploads' is not turned On - $documentationlink");
     }
 
+    if (is_float_problem()) {
+        print_error('phpfloatproblem', 'admin', '', $documentationlink);
+    }
+
     if (empty($CFG->prefix) && $CFG->dbfamily != 'mysql') {  //Enforce prefixes for everybody but mysql
         error('$CFG->prefix can\'t be empty for your target DB (' . $CFG->dbtype . ')');
     }

lang/en_utf8/admin.php

@@ -565,6 +565,7 @@ $string['performance'] = 'Performance';
 $string['pgcluster'] = 'PostgreSQL Cluster';
 $string['pgclusterdescription'] = 'PostgreSQL version/cluster parameter for command line operations. If you only have one postgresql on your system or you are not sure what this is, leave this blank.';
 $string['php50restricted'] = 'PHP 5.0.x has a number of known problems, please upgrade to 5.1.x or downgrade to 4.3.x or 4.4.x';
+$string['phpfloatproblem'] = 'Detected unexpected problem in handling of PHP float numbers - $a';
 $string['pleaseregister'] = 'Please register your site to remove this button';
 $string['pleaserefreshregistration'] = 'Your site has been registered with moodle.org, please consider updating the registration if significant changes happened since your last update, on $a';
 $string['plugins'] = 'Modules';

lib/adminlib.php

@@ -749,6 +749,18 @@ function admin_critical_warnings_present() {
     return $SESSION->admin_critical_warning;
 }
 
+/**
+ * Detects if float support at least 10 deciman digits
+ * and also if float-->string conversion works as expected.
+ * @return bool true if problem found
+ */
+function is_float_problem() {
+    $num1 = 2009010200.01;
+    $num2 = 2009010200.02;
+
+    return ((string)$num1 === (string)$num2 or $num1 === $num2 or $num2 <= (string)$num1);
+}
+
 /**
  * Try to verify that dataroot is not accessible from web.
  * It is not 100% correct but might help to reduce number of vulnerable sites.