Backslash operator on bad inputs causes segfaults

[GeorgeXing]

Using the \ operator on matrices with unequal numbers of rows causes segfaults to appear (not always in the same place). An example transcript:

julia> A = rand(2,3); b = rand(1,4)
0.91206938232058632 0.54042487514107229 0.06639860694511301 0.45407035177558663 

julia> A \ b
2.12491438834975988 0.29000399043165048 -0.44064826960265002 1.10118494911718057 

julia> A
0.41408160823125217 0.12696871086821648 0.0105299806962571 
0.34489290137506634 0.80644665662943371 0.96747404070762699 

julia> A[:,:]
0.41408160823125217 0.12696871086821648 0.0105299806962571 
0.34489290137506634 0.80644665662943371 0.96747404070762699 

julia> b
0.91206938232058632 0.54042487514107229 0.06639860694511301 0.45407035177558663 

julia> b[:,:]Segmentation fault

(Often, this will segfault on the A[:,:] call, and it sometimes doesn't segfault at all.) I suspect that this is simply a result of the code for the \ operator not checking that the inputs have the same number of rows.