Added regtests for metadynamics

regtest/rt10/COLVAR.reference

+#! FIELDS time mu1 vol md.bias
+ 0.000000  0.000 127.933  0.000
+ 0.050000  0.000 127.933  1.000
+ 0.100000  0.000 127.933  2.000
+ 0.150000  0.000 127.933  3.000
+ 0.200000  0.000 127.933  4.000

regtest/rt10/HILLS.reference

+     0.000      0.000000000    127.932640011      0.100000000      0.200000000      1.000000000   1.000 
+     0.050      0.000000000    127.932640011      0.100000000      0.200000000      1.000000000   1.000 
+     0.100      0.000000000    127.932640011      0.100000000      0.200000000      1.000000000   1.000 
+     0.150      0.000000000    127.932640011      0.100000000      0.200000000      1.000000000   1.000 
+     0.200      0.000000000    127.932640011      0.100000000      0.200000000      1.000000000   1.000 

regtest/rt10/Makefile

+../scripts/test.make
\ No newline at end of file

regtest/rt10/config

+type=driver
+# this is to test a different name
+arg="--plumed plumed.dat --stride 10 --timestep 0.005 trajectory.xyz --dump-forces forces --dump-forces-fmt=%10.6f"

regtest/rt10/plumed.dat

+mu1: DIPOLE GROUP=1-10
+vol: VOLUME 
+
+METAD ARG=mu1,vol SIGMA=0.1,0.2 HEIGHT=1.0 PACE=10 LABEL=md
+
+PRINT ...
+  STRIDE=1
+  ARG=mu1,vol,md.bias 
+  FILE=COLVAR FMT=%6.3f
+... PRINT
+
+FLUSH STRIDE=100
+
+ENDPLUMED
+