added the .s .z and .e file test methods for Str

src/builtins/Str.pir

@@ -216,6 +216,46 @@ Returns the identify value.
     .return ($S0)
 .end
 
+=item File Test Methods
+
+These return various information about the file.
+
+=cut
+
+.namespace ['Str']
+.sub 'e' :method
+    #does it exist?
+    .local string filename
+    filename = self
+    $I42 = stat filename, 0
+    if $I42 goto lisreal
+    $P0 = get_hll_global ['Bool'], 'False'
+    .return ($P0)
+  lisreal:
+    $P0 = get_hll_global ['Bool'], 'True'
+    .return ($P0)
+.end
+
+.sub 'z' :method
+    #is the length of this file zero?
+    .local string filename
+    filename = self
+    $I42 = stat filename, 1
+    if $I42==0 goto worthnothing
+    $P0 = get_hll_global ['Bool'], 'False'
+    .return ($P0)
+  worthnothing:
+    $P0 = get_hll_global ['Bool'], 'True'
+    .return($P0)
+.end
+
+.sub 's' :method
+    #how big is the file (in bytes)?
+    .local string filename
+    filename = self
+    $I42 = stat filename, 1
+    .return($I42) #if we need a conditional to return a special type of False instead of just 0, then look up
+.end
 
 =back