[boost] [build] msvc.write_setup-script always called for msvc-12.0

Subject: [boost] [build] msvc.write_setup-script always called for msvc-12.0
From: Peter Dimov (lists_at_[hidden])
Date: 2015-01-02 16:21:36

When I do (for example)

C:\Projects\boost-git\boost\tools\boostdep\build>b2 toolset=msvc-8.0

I get

...found 1 target...
...updating 1 target...
msvc.write-setup-script 
C:\Users\PETERD~1\AppData\Local\Temp\b2_msvc_12.0_vcvarsall_x86.cmd
...updated 1 target...
...found 1 target...
...updating 1 target...
msvc.write-setup-script 
C:\Users\PETERD~1\AppData\Local\Temp\b2_msvc_12.0_vcvarsall_x86_amd64.cmd
...updated 1 target...
...found 1 target...
...updating 1 target...
msvc.write-setup-script 
C:\Users\PETERD~1\AppData\Local\Temp\b2_msvc_8.0_vcvarsall_x86.cmd
...updated 1 target...
...found 1 target...
...updating 1 target...
msvc.write-setup-script 
C:\Users\PETERD~1\AppData\Local\Temp\b2_msvc_8.0_vcvarsall_x86_amd64.cmd
...updated 1 target...

which correctly generates the setup scripts for the specified msvc-8.0, but 
also unconditionally generates the setup scripts for msvc-12.0, which are 
not needed at this time.

This msvc-12.0 generation occurs even if I use a non-msvc toolset, or even 
just do b2 --show-libraries.

C:\Projects\boost-git\boost>b2 --show-libraries
...found 1 target...
...updating 1 target...
msvc.write-setup-script 
C:\Users\PETERD~1\AppData\Local\Temp\b2_msvc_12.0_vcvarsall_x86.cmd
...updated 1 target...
...found 1 target...
...updating 1 target...
msvc.write-setup-script 
C:\Users\PETERD~1\AppData\Local\Temp\b2_msvc_12.0_vcvarsall_x86_amd64.cmd
...updated 1 target...
The following libraries require building:
    - atomic
    - chrono
    [...]