TAJO-1132: More detailed version info in tsql.

Closes #211
TAJO-1114: Improve ConfVars (SessionVar) to take a validator interface to check its input. (Jihun Kang via hyunsik)

Closes #214
TAJO-1114: Improve ConfVars (SessionVar) to take a validator interface to check its input. (fixed compilation error)
Fixed a missed compilation error in TestValidators.
Revert "Fixed a missed compilation error in TestValidators."

This reverts commit b3749a0931e4e2c5447d9ce4cdfe43245300ef61.
Revert "TAJO-1114: Improve ConfVars (SessionVar) to take a validator interface to check its input. (fixed compilation error)"

This reverts commit 7a65763554e556498b6d52dd2685636c3b6584b3.
Revert "TAJO-1114: Improve ConfVars (SessionVar) to take a validator interface to check its input. (Jihun Kang via hyunsik)"

This reverts commit ee89c65b44142ca640020339e7ab5a608c1a8bf9.
TAJO-1140: Separate TajoClient into fine grained parts.

Closes #213
TAJO-1114: Improve ConfVars (SessionVar) to take a validator interface to check its input. (Jihun Kang via hyunsik)

Closes #218