weak-lens issues & updates in simulation

[RickKessler]

Recently noticed that the lensing option
LENSING_PROBMAP_FILE: $SNDATA_ROOT/models/lensing/LENSING_PROBMAP_LogNormal+MICECATv1.DAT

has rms scatter of 0.035*z instead of the expected 0.055 * z,
and there was no diagnostics to show this.

Also need LENSDMU and LENSDMU_ERR, analogous to VPEC and VPEC_ERR.

[RickKessler]

Added better init-diagnostics to show STDDEV vs. redshift in stdout.
Thus scaling the LENSDMU shifts with
WEAKLENS_DMUSCALE 1.5
results in this stdout:

 Found 7217 total rows in file. 
 Convert 7200 lens-table rows into 36(z) x 200(DMU) array
	 <dmu>[z=0.505] =  -7.3207e-04   STDDEV = 0.026
	 <dmu>[z=1.005] =  -1.7950e-04   STDDEV = 0.053
	 <dmu>[z=1.505] =  -2.1131e-05   STDDEV = 0.090
	 <dmu>[z=2.005] =   2.4553e-06   STDDEV = 0.117
	 <dmu>[z=2.505] =   4.4369e-06   STDDEV = 0.139
	 <dmu>[z=3.005] =   6.5424e-06   STDDEV = 0.159
	 <dmu>[z=3.505] =   1.0157e-05   STDDEV = 0.176
 Done initializing Prob(-2.274 < DeltaMU < 0.319) 
   in 36 redshfit bins from 0.405 to 3.905 
 LENSDMU_SCALE   = 1.50 
 LENSDMU_ERR     = 0.50 * LENSDMU 

[RickKessler]

Added sim-input
WEAKLENS_DMUERR_FRAC:

which defines LENSDMUERR = frac * LENSDMU

In snana.exe & snlc_fit.exe, the smeared LENSDMU and uncertainty LENSDMUERR are read from the sim data files and written to output SNANA/FITRES table file.

The next step is to correct distance and inflate uncertainty using LENSDMU[ERR]; there are two possibilities here:
(i) read into BBC and correct fitted distance MU -> MU - LENSDMU and MUERR += LENSDMUERR in quadrature (and other post-LCFIT analysis codes have to replicate)
(ii) correct mB and mBERR in output so that BBC or any other method gets this info

[benjaminrose]

From how I am reading this, option (ii) would better match observations since we can't easily subtract out weak lensing effects.