- fixed out-of-bounds memory accesses in nvBWT
- added possibility to specify genome index to sufsort-test

[git-p4: depot-paths = "//sw/gpgpu/nvbio/main/": change = 18185737]
make sure the random symbol generator generates a valid symbol

[git-p4: depot-paths = "//sw/gpgpu/nvbio/main/": change = 18186065]
fixed pac saving

[git-p4: depot-paths = "//sw/gpgpu/nvbio/main/": change = 18186192]
enable longer strings

[git-p4: depot-paths = "//sw/gpgpu/nvbio/main/": change = 18186196]
restored option to save more efficient "wpac" files

[git-p4: depot-paths = "//sw/gpgpu/nvbio/main/": change = 18187242]
better exception handling

[git-p4: depot-paths = "//sw/gpgpu/nvbio/main/": change = 18191356]