Previously, if `--resource-path` were used multiple times, the last
resource path would replace the others.
With this change, each time `--resource-path` is used, it prepends
the specified path components to the existing resource path.
Similarly, when `resource-path` is specified in a defaults file,
the paths provided will be prepended to the existing resource
path.
This change also allows one to avoid using the OS-specific path
separator; instead, one can simply use `--resource-path`
a number of times with single paths. This form of command
will not have an OS-dependent behavior.
This change facilitates the use of multiple, small defaults
files: each can specify a directory containing its own
resources without clobbering the resource paths set by
the others.
Closes#6152.
735a69de6b