Fix #23 (${} string interpolation syntax is deprecated)

We are careful not to replace the variable variables (never a good idea
to use this "feature"), nor the special `preg_replace()` syntax (which
is not deprecated).

includes/calendar.php

@@ -780,7 +780,7 @@ function easter_date($year) {
     } else $zindex = '';
 
     if($columns) $o .= '<td class="months_in_columns">'."\n";
-    $o .= "<table class='${size}calendar_main'$zindex>\n";
+    $o .= "<table class='{$size}calendar_main'$zindex>\n";
 
     // 1st row: headline with month and year (year only if needed)
     //============================================================
@@ -950,7 +950,7 @@ function easter_date($year) {
 
         $x = $calendar_cf['dont_underline_longevents']? '2':'';
 
-        $showtoday   =  $i == $today       ?  " ${size}calendar_today"        : '';
+        $showtoday   =  $i == $today       ?  " {$size}calendar_today"        : '';
         $shortevent  =  $i == $shortevent  ?  " calendar_shortevent"          : '';
         $startevent  =  $i == $startevent  ?  " calendar_startevent$x"        : '';
         $midevent    =  $i == $midevent    ?  " calendar_midevent$x"          : '';
@@ -959,7 +959,7 @@ function easter_date($year) {
         $startevent3 =  $i == $startevent3 ?  " calendar_startevent3"         : '';
         $midevent3   =  $i == $midevent3   ?  " calendar_midevent3"           : '';
         $endevent3   =  $i == $endevent3   ?  " calendar_endevent3"           : '';
-        $birthday    =  $i == $birthday    ?  " ${size}calendar_birthday"     : '';
+        $birthday    =  $i == $birthday    ?  " {$size}calendar_birthday"     : '';
         $holiday     =  $i == $holiday     ?  " calendar_holiday"      : '';
 
 

includes/calendarconfig.php

@@ -508,7 +508,7 @@ function openedit(button,hidearea,clicktext,reclicktext,displaytype,antihidearea
 for ($i = 0;$i <=50 ;$i++ ) {
 	$selected = '';
 	if($i.'px' == $dayspacing) {$selected = ' selected'; $j = 1;}
-	$spacingvalues_select .= "<option value='${i}px' $selected>${i}px</option>\n";
+	$spacingvalues_select .= "<option value='{$i}px' $selected>{$i}px</option>\n";
 }
 $preselect = $j? '' : '<option value="'.$dayspacing.'" selected>' . $dayspacing . '</option>';
 if($bordercollapse=='collapse' || !$dayspacing) $preselect = "<option value='0px' selected>0px</option>\n";