procToArgv calls doesFileExist instead of checking for a slash

[kirelagin]

execvp work by checking for a slash in the path; if there is a slash, it assumes it is a path (absolute or relative), if there is no slash, it looks it up in PATH.

Therefore the current behaviour of procToArgv can be unexpected in that if you run echo while having a file called echo in current directory, it will run your file, while execvp will resolve it through PATH.

Open question: will execv accept a relative path? If it will, the fix is easy, if it will not, we’ll also have to resolve relative paths.