First crack at adding comprehensive LineSearch objects to SNES.

Hg-commit: 5d4c4dee0f60ddbc6ca02bd6d0b7e262bffb5bac

merge SNES/DM refactor

Hg-commit: 31d66a4917111e3b9e87bf19170c2c9421b4e8be

Refactor SNES DM infrastructure

The residual and Jacobian function pointers are now stored in a managed
context on the DM. Coarsening of this context is handled by a
DMCoarsenHook, so the coarse lev

Refactor SNES DM infrastructure

The residual and Jacobian function pointers are now stored in a managed
context on the DM. Coarsening of this context is handled by a
DMCoarsenHook, so the coarse level DM automatically has function
pointers for residual evaluation. The SNESDM context (attached to a DM)
has copy-on-write semantics for all DMs other than the one it was
originally created on. That means that changes to the function pointers
from the fine level are automatically propagated unless a coarse level
is changed manually.

Hg-commit: ce0066853e1ef4402603a33070cb3bfd75c87f86

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Added lagged-jacobian and line-search weighting to the initial inverse Jacobian in QN.

Hg-commit: b27935e86d42cf1ef02c71c5239ae48ba90dcb62

Changed the name of "secant" line search to the more accurate "critical"

Hg-commit: 8c0d6f59a1049c232aff6f95855cf0b66563b9c4

Ensure that obj->ops->destroy is zeroed in XXSetType() after the old implementation has been destroyed.

There are circumstances where VecSetType() is called more than once to
change the type without

Ensure that obj->ops->destroy is zeroed in XXSetType() after the old implementation has been destroyed.

There are circumstances where VecSetType() is called more than once to
change the type without an intervening XXCreate_YY(). An example is
changing to VECSEQCUSP via VECCUSP.

Hg-commit: 1262149b3e206062ad0b002925300684fd3420e8

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added SNESLineSearchApply(), SNESLineSearchPreCheckApply() and SNESLineSearchPostCheckApply() to the interface

Hg-commit: 2c13a8e4d8b8ac5f9278109127dbdacc4d0d6da6

added SNESSetFunctionNorm and SNESSetIterationNumber to make SNESShells easier to write.

Hg-commit: 35d4b2bf7a9aec9ffb7973f65f13044a16facf27

Add SNESMS: multi-stage smoothers, a nonlinear analogue to polynomial smoothers

Hg-commit: 3de9c70f2af1c2a7d27b25f3ed88b30b58a24e48

Just call VecDestroyVecs()

Hg-commit: 3f6eded5c46256ca06ca2b2c40af254ecb0a1850

removed snes_use_gs and snes->usegs; use SNESGS instead now

Hg-commit: 33cdc58540214fb127aed640a53850526359edf5

FAS now is totally built of composed solver components

Hg-commit: 7c951068ce41b208bd8fb528eeb92b7852805722

added SNES type gs

Hg-commit: 1e0e22b4b634cef37972a39e681106160bd1486b

Mass revert file modes that were made executable in f6e61ee9c329

Hg-commit: 116d90d0b66125cee0db3e7351047057e756baf5