Disable add database button if no versions available

[jgfoster]

Application Specific Information:
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'copy from /Users/calebherbel/Library/GemStone/GemStone64Bit(null)-i386.Darwin/bin/extent0.dbf to /Users/calebherbel/Library/GemStone/db1/data/extent0.dbf failed because Error Domain=NSCocoaErrorDomain Code=260 "The file “extent0.dbf” couldn’t be opened because there is no such file." UserInfo={NSFilePath=/Users/calebherbel/Library/GemStone/GemStone64Bit(null)-i386.Darwin/bin/extent0.dbf, NSUnderlyingError=0x6000003feac0 {Error Domain=NSPOSIXErrorDomain Code=2 "No such file or directory"}}!'
terminating with uncaught exception of type NSException
abort() called

Application Specific Backtrace 1:
0 CoreFoundation 0x00007fff3e913ded __exceptionPreprocess + 256
1 libobjc.A.dylib 0x00007fff6a9df720 objc_exception_throw + 48
2 CoreFoundation 0x00007fff3e913c1f +[NSException raise:format:] + 201
3 GemStone 0x000000010f5b4656 -[Database installExtentA:] + 678
4 Foundation 0x00007fff40bb8104 NSThread__start + 1218
5 libsystem_pthread.dylib 0x00007fff6bca1305 _pthread_body + 126
6 libsystem_pthread.dylib 0x00007fff6bca426f _pthread_start + 70
7 libsystem_pthread.dylib 0x00007fff6bca0415 thread_start + 13