Fix error message for missing fld files

This should fix #35, which is related to some Hdf5 errors being displayed instead of a nice error message when we try to use an .fld file which does not exist.

See merge request !689

Improve performance of incompressible solver

This MR contains improvements to the performance of the incompressible solver (some of the changes might also help in other cases).

I worked on these changes based on a profiling of the `Cyl.xml` example (2D, N=5, using both tris and quads). For this particular case (in serial), I got a reduction of computational cost close to 30%, although I suspect simulations with higher order or in 3D will get more modest improvements.

The main changes are:

- Use a virtual function to make UnsteadySystem skip the FwdTrans it performs after each time step, since this is completely redundant for the incompressible solver
- Introduce a parameter to choose the frequency at which the solver checks for NaNs
- Tweak the default value of the mdswitch parameter for the multilevelstaticcond, and also allow to specify it in the session file
- Include PhysDeriv in a single direction in the Collections, since we need it to compute div(u) for the pressure forcing
- Use symmetric matrices for the interior part of the static cond (whenever possible)
- Several small changes to reduce overhead costs, especially in matrix vector multiplications.


See merge request !645

Fix time-integration for VCSMapping

This fixes some inconsistencies in VCSMapping which prevented it from achieving 2nd order accuracy in time.

See merge request !687

Added missing GetRowComm in AllReduce call.

This MR fixes the IterativeFull solver to work in parallel.

See merge request !685

Conflicts:
	CHANGELOG.md

Fix/changelog

This just adds missing entries to the changelog. When cherry-picked to the release branch this should also remove a duplicate header which appeared there for v4.3.4.

See merge request !686

Chris Cantwell authored Aug 14, 2016 and Douglas Serson committed Aug 24, 2016

(cherry picked from commit 64503e575a2e56672f9eeaa88b9ec3c1074d688c)

Expansion from restart file and improved partitioning

This MR makes two changes which might be useful for simulations with variable polynomial order:
- Allow the expansions to be loaded directly from the field definitions in a restart file (issue #14), using:

```xml
<EXPANSIONS>
     <F FILE="restartfile.fld" />
</EXPANSIONS>
```
This is useful when using DriverAdaptive, since in that case the final distribution of polynomial orders is only available in the field file.

- Introduce new options for load balancing in the mesh partitioning, through the solver info `WEIGHTPARTITIONS`. Possible values are `DOF` (load balanced by number of degrees of freedom in each element), `BOUNDARY` (load balanced by number of boundary degrees of freedom in each element) or `BOTH`. By default, the current behaviour of using no weights is maintained. 


See merge request !617

Fix OCE third-party URL

This MR fixes the OCE third-party URL in the CMake configuration.

See merge request !681

# Conflicts:
#	CHANGELOG.md

Add support for Gmsh high-order output

This MR primarily adds support for Gmsh output at arbitrarily high-order for quads, hexes, triangles and tetrahedra, and up to order 4 output for prisms.

See merge request !679