Protect against multiple specification of same inputs option

[nataraj2]

This PR adds a routine to the ParameterSanityChecks that will detect if any of the options have been specified mutliple times in the inputs, and if yes, it will abort after printing all the occurences. This prevents accidental multiple inputs specifications by the user. An example output is

Duplicate input: amr.v (2 occurrences)
amrex::Abort::1::Duplicate inputs detected !!!
SIGABRT
amrex::Abort::3::Duplicate inputs detected !!!
Duplicate input: erf.substepping_type (2 occurrences)
Duplicate input: geometry.is_periodic (2 occurrences)
Duplicate input: fabarray.mfiter_tile_size (2 occurrences)
Duplicate input: max_step (3 occurrences)

[asalmgren]

I would not like to merge this PR -- I often keep multiple lines of the same input so I can easily change them without having to re-type the lines.

[nataraj2]

Change means to put "#" on one and enable another? That modification can be done on this routine. Have been bit by this issue multiple times especially with long inputs files.

[asalmgren]

Ok, that's a good point -- the comment does allow me to do what I need to do and this would protect against the user error you're seeing. We can try it

[nataraj2]

Actually the current routine allows for inputs like below without reporting duplicate errors. So, no modifications needed.

max_step = 100000
#max_step = 100000