Prepare Windows for 2.1 beta 1: installer dialogs and bump "build number".

PCbuild/BUILDno.txt

@@ -33,6 +33,8 @@ How to change the Windows build number:
 
 Windows Python BUILD numbers
 ----------------------------
+  11    2.1b1
+        28-Feb-2001
   10    2.1a2
         1-Feb-2001
    9    2.1a1

PCbuild/python20.wse

 Document Type: WSE
 item: Global
   Version=5.0
-  Title=Python 2.1 alpha 2
+  Title=Python 2.1 beta 1
   Flags=00010100
   Languages=65 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
   Japanese Font Name=MS Gothic
@@ -64,7 +64,7 @@ item: End Block
 end
 item: Set Variable
   Variable=APPTITLE
-  Value=Python 2.1 alpha 2
+  Value=Python 2.1 beta 1
 end
 item: Set Variable
   Variable=GROUP
@@ -72,7 +72,7 @@ item: Set Variable
 end
 item: Set Variable
   Variable=PY_VERSION
-  Value=2.1a2
+  Value=2.1b1
 end
 item: Set Variable
   Variable=MAINDIR

PCbuild/pythoncore.dsp

@@ -739,11 +739,11 @@ SOURCE=..\Modules\getbuildinfo.c
 
 !IF  "$(CFG)" == "pythoncore - Win32 Release"
 
-# ADD CPP /D BUILD=10
+# ADD CPP /D BUILD=11
 
 !ELSEIF  "$(CFG)" == "pythoncore - Win32 Debug"
 
-# ADD CPP /D BUILD=10
+# ADD CPP /D BUILD=11
 
 !ELSEIF  "$(CFG)" == "pythoncore - Win32 Alpha Debug"