When someone writes
#include " some_file.h "
the compiler returns "file not fond..." with fonts and quotes that may make it hard to see there are excess quotes or surprising bytes in the filename. Assuming that files are usually logically named and start and end with an alphanumeric character, we can check for the file's existence by stripping the non-alphanumeric leading or trailing characters. If the file is found, emit a non-fatal error with a fixithint.