langevin: Define DROPSUFFIX in localconf.mk
split: Some amendments related to splitdir

- Ensure to never select absolute path /splitdata.
- Make comments in standalone more comprehensible.
- Remove redundant assignment in downsampling.
- Show splitdir with showdata also in correlation.
common: Avoid circular dependency for linked data

Allow . in datadirs to use ./splitdata as splitdir
but do not search data files for linking there.
histogram: Source code histo2d.c updated

- New option -F for relative frequencies.
- Bugfix to option -r.
main: By default do not split downsampled data
scripts: Shell script cosmetics
scripts: More comprehensible variable name
scripts: Ignore newlines in data files
scripts: Exit if unit cannot be extracted from filename
correlation: More precise filename matching

Avoid mixing filenames when collecting correlation
times of different components in a single file.
cossin: Suffix .cs for cos-/sin-projected data

Shorter suffix than .cossin to save space in plot titles.
main: By default keep suffixes of projected data
histogram: Newline after filename unit in title
common: Recursive use of make on selected subdirs
doc: Recursive use of make on selected subdirs
doc: Subsections instead of subheaders
info: Recursive use of make on selected subdirs
histogram: Typo in info text
histogram: Small change for make info
drift: Basic structure

Directory for analysis of stationary drift fields
(binned averages of differential quotients).