Revert "Fixed headers bug in FileWritersPool."

This reverts commit dd6c3b8c646a25b96d587126290f9684c5e34925.
Revert "Fixed bug whe closing files in FileWritersPool"

This reverts commit 2f2e92330440a2359e4fbc7e83acc42f6682c84e.
Revert "Fixed write headers for FileWritersPool"

This reverts commit acb8a0ac6a9d314111999ff139009d57cbe4ffe5.
Revert "Simplified interface of FileWritersPool"

This reverts commit facdcb38ae5446e21bb529f518c63eaaec8d597c.
Revert "Simplified fname formatter"

This reverts commit b0e954f4307e9fdfd6f609ccb911f0748989c9fe.
Revert "Added output filename template argument for csvsplit when reading from STDIN."

This reverts commit 1f0178eb88444cf7b71266fd0125c99bdfebb2b6.
Revert "Fixed header behavior for csvsplit."

This reverts commit 1df4290ee99ae7c650e4894f54c5e46e7928f070.
Revert "csvsplit: fixed bug too many open files"

This reverts commit 09f415cf2c63b9962e2be383215022450410f9c9.
Merge